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FOUS11 KWBC 050920
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
418 AM EST Sat Mar 05 2022

Valid 12Z Sat Mar 05 2022 - 12Z Tue Mar 08 2022

...Western U.S....
Days 1-2...
An upper low will continue to drop southeast across California
into southern Nevada today before pivoting east toward the Four
Corners region tonight into early Sunday. This will support high
elevation snows from the California mountains through the Great
Basin and portions of the Southwest into the central Rockies.
Some of the heaviest accumulations are expected to occur across
the mountains of central Nevada, where low-to-mid level
frontogenesis along with favorable upper forcing is expected to
support widespread totals of 4 to 8 inches, with local
accumulations of a foot or more across the region.

This low is forecast to transition to an open wave and move east
of the Rockies into the High Plains, but not before producing at
least some light to moderate snow accumulations across the central
Rockies on Sunday. Meanwhile, a northern stream shortwave
dropping south from western Canada is expected to produce some
light to moderate snow accumulations across the northern Rockies
late Sunday into early Monday.

...Central Plains and Upper Midwest through the Great Lakes/New
England...
Day 1...
Precipitation associated with a low-amplitude shortwave lifting
northeast from the central Plains will continue to develop this
morning across the Upper Midwest, producing an initial round of
snow and ice across portions of eastern Minnesota, northern
Wisconsin, and northern Michigan. Some areas of northern
Wisconsin and Upper Michigan may see ice accumulations of 0.10
inch or more before this initial wave moves out by the afternoon.

Meanwhile, a more defined upstream wave will continue to lift
northeast across the Rockies and into the central High Plains this
morning. Northeasterly flow on the backside of a 700 mb low
tracking northeast across western Nebraska, overlapped by
favorable upper jet forcing, will support snow shifting east this
morning from the southeastern Wyoming and northeastern Colorado
ranges into the Nebraska Panhandle and southeastern South Dakota
later this morning. This next system will continue to amplify as
it moves from the central Plains into the Upper Midwest this
evening. A favorable upper jet couplet overlapping low-to-mid
level frontogenesis will support the development of moderate to
heavy precipitation. Thermal profiles continue to indicate a
wintry mix is likely, with significant ice accumulations across
portions of southwestern to central Minnesota, northern Wisconsin,
and Upper Michigan. This will likely bring 24 hour ice
accumulations upward over a 0.25 inch in some locations.

Farther to the east, warm advection precipitation falling out
ahead of the system is expected to fall as a wintry mix, resulting
in light snow and ice accumulations across portions of northern
New York and New England tonight into early Sunday.

...Central Plains to the Northeast...
Days 2-3...
The shortwave moving into the southern High Plains Sunday night
will be stretched northeastward through the central Plains and mid
Mississippi Valley, ahead of an amplifying northern stream trough
over the northern Plains and Upper Midwest. Favorable upper jet
forcing and strong frontogenesis will support precipitation
blossoming from the mid Mississippi Valley into the Great Lakes
and Ohio Valley Sunday night, and into the Northeast on Monday.
Along the northern edge of the precipitation shield, thermal
profiles suggest frozen precipitation is likely. Confidence in
the details is quite limited at this point, however at least some
light snow accumulations appear likely from the mid Mississippi
Valley to Lower Michigan, northern New York, and New England.

Pereira



$$




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FOUS11 KWBC 052100
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
359 PM EST Sat Mar 05 2022

Valid 00Z Sun Mar 06 2022 - 00Z Wed Mar 09 2022

...Western U.S....
Days 1-3...

The upper low currently dropping southeast across California and
the southern Great Basin will move east through Sunday across the
Four Corners region. Locally strong forcing associated with the
height falls coupled with favorably moist upslope flow will result
in areas of heavy snow for areas of the Wasatch and the central
Rockies. The heaviest accumulations are expected to be over the
southwest facing slopes of the San Juan Mountains in southwest
Colorado where amounts locally in excess of a foot are expected.
The Wasatch and Uinta Range of Utah, and the Wind River Range of
western Wyoming are likely to see totals of as much as 6 to 12
inches. For Sunday night and Monday, a new upper trough digging
down from the northern Rockies will help to gradually eject the
upper low/trough crossing the Four Corners out into the Plains. A
combination of the departing energy and the arrival of new energy
will support a few inches of new snow, and especially the Colorado
high country for this period.

Meanwhile, a new and broad upper trough will impinge on the
Pacific Northwest and the northern Rockies Monday night through
Tuesday, and a cold front will be seen dropping southeast from
Alberta and Saskatchewan. Relatively moist deep layer northwest
flow over the Washington Cascades and the northern Rockies along
with embedded shortwave energy should result in the development of orographically driven snow showers. Meanwhile, low-level
post-frontal upslope flow especially into the east-facing slopes
of the northern Rockies and far northern High Plains will be in
place by late Tuesday, and this will also couple with the moisture
and energy aloft for areas of northwest and central Montana to see
expanding areas of moderate to locally heavy snow. Snowfall
accumulations of as much as 4 to 8 inches are expected for these
areas with locally heavier totals approaching a foot by the end of
the period.


...Midwest to the Northeast...
Days 1-3...

Surface low pressure crossing the Upper Midwest this evening along
with an associated mid-level trough will advance through the Upper
Great Lakes overnight and then quickly into southeast Canada on
Sunday. An axis of snow, sleet, and freezing rain is expected
along the northwest flank of the low track. Much of the additional
freezing rain threat will extend from areas of central Minnesota
through northwest Wisconsin and across the U.P. of Michigan, and
this will tend to occur as the low-level flow begins to back
around and bring some low-level cold air back south as the low
center passes just to the south of the region. Locally heavy
precipitation will be expected as the core of the mid-level
energy/trough crosses this evening and overnight, and some of
these areas will likely see sufficient dynamic cooling arrive for
any areas of sleet and freezing rain to changeover to a period of
snow before ending Sunday morning. In fact, there is enough model
support for a swath of 2 to 3+ inch snowfall amounts from eastern
South Dakota through central Minnesota and far northwest Wisconsin
as the aforementioned upper-level support lifts northeast across
the region. Farther downstream across areas of northern New
England, and especially northern Maine, this system as it
approaches tonight will be encountering a retreating cold airmass,
but there is expected to be a burst of some accumulating snow
Sunday morning on the front end of the nose of strong warm air
advection. A brief changeover to some sleet and freezing rain is
expected too with some light icing possible before the system
gradually pulls away Sunday evening.

As this system pulls way by late Sunday, additional energy
ejecting out across the central Plains will already be driving the
development of a new wave of low pressure across the middle
Mississippi Valley which will then very quickly move into Ohio
Valley by Monday morning and then New England by Monday evening.
Sufficient low-level cold air is expected to be in place to the
northwest of the low track to favor a swath of some light freezing
rain from parts of northern Illinois east-northeastward through
southern lower Michigan and the interior of New York and northern
New England. To the northwest of this axis, sufficiently deep
enough cold air will in place for a swath of light snow with 2 to
3+ inch amounts expected from areas of northeast Iowa, southern
Wisconsin and northern lower Michigan. Some light snow
accumulations will also be expected for areas of northern New
England with this next wave before it exits the Northeast Monday
night.

Orrison



$$




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FOUS11 KWBC 060905
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
403 AM EST Sun Mar 06 2022

Valid 12Z Sun Mar 06 2022 - 12Z Wed Mar 09 2022

...Western U.S....
Days 1-3...
An upper low will continue to move across the Southwest into the
Four Corners region this morning before transitioning to an open
wave as it moves across the Rockies and into the High Plains later
today. The associated mid-to-upper level dynamics will likely
support additional snows across the Colorado and far northern New
Mexico ranges, with WPC probabilities indicating widespread
potential for snowfall accumulations 4-8 inches across the higher
terrain. Locally heavier accumulations are most likely across the
San Juan and Sangre de Cristo mountains, where the probabilities
for 8 inches or more are highest.

The potential for significant snowfall accumulations is likely to
wane by Sunday night as the shortwave continues to progress
through the Plains. Meanwhile, a northern stream shortwave
dropping south from western Canada will support some light
accumulations over the northern Rockies before returning the
change for light accumulations back into the central Rockies on
Monday.

Beginning Monday night, and continuing through Tuesday into early
Wednesday, a broader scale trough is forecast to amplify south
across the Pacific Northwest and northern Rockies -- bringing much
colder air into the region. Increasing low-to-mid level
frontogenesis overlapped by left-exit region upper jet forcing
will increase the potential for heavy snow from the northern
Cascades to the northern Rockies. Across the Northwest, WPC
probabilities indicate accumulations of 4-8 inches are likely,
with local accumulations of a foot or more possible across the
higher elevations of the northern Cascades and the Blue Mountains
by early Wednesday. Across the Rockies, accumulations of 4-8
inches are likely from the northern Idaho and western Montana
ranges to the northern Utah mountains. Local accumulations of a
foot or more are most likely in the northern Idaho ranges,
including the Bitterroot and Clearwater mountains.

...Northeast...
Days 1...
Warm advection precipitation ahead of a well-defined system moving
across the Upper Great Lakes will continue to spread across
northern New York and New England this morning. Falling initially
as a wintry mix, light ice accumulations are possible from
northern New York through northern Vermont and New Hampshire into
northern Maine. Across northern Maine where the deeper colder air
is expected to remain in place a little bit longer, a few inches
of snow is possible before changing over to a wintry mix and rain
later today.

...Central Plains to the Northeast...
Days 1-3...
The upper trough moving into the central Plains Sunday night is
forecast stretch northeastward ahead of an amplifying northern
stream trough over the Upper Midwest. Ample moisture advection
afforded by deep southwesterly flow will support an expanding area
of precipitation from the mid Mississippi Valley into the Great
Lakes and Ohio Valley Sunday night and Monday morning. Low-to-mid
level frontogenesis along with cooling temperatures will support
snow developing on the northwest side of the associated surface
low as it tracks northeastward from the mid Mississippi Valley
toward the Great Lakes Sunday night. Light snow accumulations are
expected from as far west as southeastern Nebraska and
northeastern Kansas, spreading east across northern Missouri and
Iowa into northern Illinois and southern Wisconsin by Monday
morning. Snow is expected to continue east across northern Lower
Michigan, with right-entrance region upper jet forcing providing a
slightly greater potential for heavier accumulations. The low is
forecast to continue northeastward near the Lower Great Lakes and
into the Northeast on Monday. This will bring the next chance for
a wintry mix, with some light snow and ice accumulations, back
into northern New York and New England.


Pereira


$$




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FOUS11 KWBC 062039
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
337 PM EST Sun Mar 06 2022

Valid 00Z Mon Mar 07 2022 - 00Z Thu Mar 10 2022

...Western U.S....
Days 1-3...

A new northern stream upper trough digging down from the northern
Rockies will help to gradually eject the current upper low/trough
crossing the Four Corners out into the Plains. A combination of
the departing energy and the arrival of new energy will support a
few inches of new snow tonight through Monday, and especially the
Colorado high country. This additional intrusion of northern
stream energy should then exit southeastward gradually out into
the Plains on Tuesday.

Meanwhile, a new and broad upper trough will impinge on the
Pacific Northwest and the northern Rockies Monday night through
Tuesday, and an Arctic cold front will be seen dropping southeast
from Alberta and Saskatchewan. Relatively moist deep layer
northwest flow over the Washington Cascades and the northern
Rockies along with embedded shortwave energy should result in the
development of orographically driven snow showers. Meanwhile, with
the cold front itself, there will be rather strong forcing and
sufficiently steep enough lapse rates/shallow instability for a
rather high chance of seeing snow squalls along and immediately
behind the frontal passage. Linear bands of snow squalls should
advance down from northwest to central Montana Monday evening and
will support some brief intense snowfall rates that could reach
1"+/hour. Low-level post-frontal upslope flow into the east-facing
slopes of the northern Rockies and northern High Plains will be in
place moving forward going through Tuesday, and this coupled with
the mid-level moisture fetch and energy aloft will favor an
expansion of areas of moderate to heavy orographically focused
snowfall across northwest and central Montana. As the overall
upper trough and focus of shortwave energy advances further south
into the Intermountain Region Tuesday and Tuesday night, there
will also be heavy snow spilling over into the Bitterroots,
Sawtooth and Blue Mountains as well. Snowfall accumulations of as
much as 4 to 8 inches are expected for the region with locally
heavier totals approaching a foot by early Wednesday for the
favored higher peaks.

On Wednesday, the upper trough will be broadening further down to
the south across the Intermountain Region and into the central
Rockies, and this will allow for areas of heavy snow to begin
focusing down across the favored terrain of western Wyoming,
northern Utah and northwest Colorado. This will include the
Tetons, Wind River Range, Uinta and Wasatch ranges. The northwest
Colorado high country will also see heavy snow arrive. Rather
divergent flow aloft associated the approach of the upper trough,
coupled with mid-level moisture and orographics will favor some
snowfall totals in the 4 to 8 inch range with isolated totals
approaching a foot by Wednesday night. Low pressure will also be
developing over the Colorado High Plains by early Wednesday as the aforementioned cold front continues to settle southward.
Post-frontal east-northeast flow into High Plains of southeast
Wyoming including the Laramie Range and the ejecting energy from
the upstream trough will allow snow to develop and spread east
across these areas as well, with the snow advancing out into far
southwest South Dakota and much of central and western Nebraska.
Several inches of snow is expected by late Wednesday across these
areas with the Laramie Range likely seeing some amounts exceeding
8 inches.


...Central Plains to the Lower Great Lakes and New England...
Days 1-2...
The mid-level closed low currently advancing east through the Four
Corners area will advance out across the central Plains this
evening and will generate a new area of low pressure along the
front across the middle Mississippi Valley which will then very
quickly move into Ohio Valley by Monday morning and then New
England by Monday evening. A nose of at least some modest elevated
instability coupled with strong forcing/vort energy associated
with the ejecting trough should foster an axis of convectively
driven precipitation across areas of the central Plains and lower
Missouri Valley this evening with snow, sleet and freezing rain
expected. This will include the Kansas City metropolitan area
where some brief heavy snow is expected and potentially a couple
of inches of accumulation. As the energy lifts northeastward
overnight and Monday, there should be a swath of 2 to 4 inch
snowfall amounts extending across northwest Missouri,
southern/eastern Iowa, southern Wisconsin, northern Illinois and
lower Michigan. Just to the south of this snowfall axis, but to
the northwest of the low track, the cold air will be more shallow
and these areas should see a swath of some sleet and light
freezing rain. As the low tracks into New England by Monday
evening, some light icing concerns will also be noted across parts
of western and northern New York, and northern New England. Some
snow is expected for areas of northwest Maine where the cold will
be a bit deeper, and locally several inches are expected here
going through Monday night.

Orrison

$$




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FOUS11 KWBC 070923
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
421 AM EST Mon Mar 07 2022

Valid 12Z Mon Mar 07 2022 - 12Z Thu Mar 10 2022

...Great Lakes and Northeast...
Day 1...
Deformation band associated with a shortwave lifting northeast out
of the central Plains will continue to shift east into the Upper
Great Lakes this morning. Favorable upper jet forcing overlapping
low-to-mid level frontogenesis will support light to moderate snow
spreading from southern Wisconsin to central and northern Lower
Michigan this morning. WPC probabilities indicate that at least a
few additional inches of snow are likely across central Michigan,
with a slight risk for additional accumulations of 4 inches or
more after 12Z.

Meanwhile, warm advection precipitation ahead of the system will
spread into the Northeast later this morning, falling as a wintry
mix across northern New York and New England. While many areas
may change over to rain, a transition back to snow on the
northwest side of the low can be expected across some areas as the
low tracks across the Northeast this evening. Minor ice
accumulations can be expected across northern New York and New
England, with a few inches of snow possible along the U.S.-Canada
border.

...Western U.S....
Days 1-3...
Beginning tonight and continuing through Wednesday, a steady
stream of embedded shortwaves will amplify a broader scale trough
across the Pacific Northwest and northern Rockies. Favorable
upper forcing along with increasing low-to-mid level frontogenesis
will support the increasing potential for heavy mountain snow from
the northern Cascades to the northern Rockies. In the Pacific
Northwest, accumulations of 4-8 inches are likely across the
higher elevations of the Cascades and Blue Mountains, with some
potential for accumulation of a foot or more across the high
terrain by Tuesday. Along the Rockies, accumulations of 4-8
inches are likely from the northern Idaho and southwestern Montana
ranges to the central and western Wyoming and northern Utah
ranges. Locally heavier accumulations of up to a foot or more are
possible, especially across the northern Idaho ranges, including
the Bitterroot and Clearwater mountains.

Models show an amplifying shortwave digging southeast from the
Pacific Northwest into the Great Basin Wednesday night. This will
shift the greater potential for heavier snow farther south into
the central Rockies. Favorable upper forcing along with the
southward moving low-to-mid level baroclinic zone will increase
the potential for snow accumulations of 4-8 inches across the Utah
and western Colorado ranges.

...Central Plains...
Day 3...
As the upper trough in the West continues to amplify and dig
southeast, a low-to-mid level low is forecast to drop southeast
into the central High Plains, encouraging inflow into a downstream
boundary over the Plains. Thermal profiles support snow across
northern Kansas and Nebraska. While differences in the details
remain, overnight model guidance has moved toward a stronger
consensus, indicating that impactful snow is likely for portions
of the central Plains on Wednesday continuing into Thursday. By
early Thursday WPC probabilities indicate that accumulations of 4
inches or more are likely across much of western and central
Nebraska.

Pereira

$$




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FOUS11 KWBC 072021
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
321 PM EST Mon Mar 07 2022

Valid 00Z Tue Mar 08 2022 - 00Z Fri Mar 11 2022

...Northeast & Mid Atlantic...
Days 1-2...
The first storm system to impact the Northeast will be
strengthening as it tracks across central Maine this evening.
Strong vertical motion beneath the right-entrance region of a
250mb jet streak will be positioned over northern Maine.
Meanwhile, 850-700mb frontogenesis will result in a band of
heavier snowfall between 00-06Z tonight. WPC's Snowband
Probability Tracker (SPT) does show a narrow deformation zone
where snowfall rates over 1"/hr are possible. Meanwhile, just to
the south, sub-freezing temperatures at the surface and warm
southerly flow several thousand feet up will result in a profile
favorable for freezing rain. Given the storm's fast progression,
ice accumulations will generally remain below a tenth of an inch
across north-central Maine.

Focus then shifts to an upper trough ejecting out of the Four
Corners region early Tuesday morning that quickly tracks across
the South Central U.S. by Tuesday afternoon. As WAA increases
within the 850-500mb layer out ahead of the neutrally-tilted upper
trough, the 250mb jet streak over the Northeast eventually exceeds
150 kts by 06Z Wednesday. Precipitation is forecast to breakout in
the Mid-Atlantic and the central Appalachians as vertical motion
becomes increasingly robust. Boundary layer temperatures will be
above freezing but drier dew points are expected, which combined
with stronger vertical ascent into the column will result in
dynamic cooling and temperatures wet-bulbing to just below
freezing west of I-95. Elevation will play a critical role in
accumulations given the milder boundary layer conditions along and
just west of I-95 and recent warmth over the last few days. Latest
WPC probabilities indicate up to a 20% chance for >4" of snowfall
in the highest elevations of western Virginia, eastern West
Virginia, and points north into western Maryland and central
Pennsylvania. It is worth noting there have been recent trends in
guidance that suggest the potential for banding in the vicinity of
the 850-700mb front over northern Virginia and into northern
Maryland. Should this occur, heavier rates could lead to increased
snowfall accumulations in future forecasts, especially in the Blue
Ridge and central Appalachians.

...Western U.S....
Days 1-3...
A pair of shortwave troughs will amplify a broader scale trough
that is set to track through the Northwest on Day 1, dig into the
central Rockies and as far west as the Great Basin on Day 2, and
amplify further into the Four Corners region by Day 3. As the
broader scale trough deepens, diffluent 700-500mb flow will
support the development of snow from the Cascades to the Northern
Rockies on Day 1. Localized accumulations exceeding a foot are
possible, especially across the northern Idaho ranges, including
the Bitterroot and Clearwater mountains. As a strong area of high
pressure in the Canadian Prairies also dives south on Day 2,
easterly upslope flow and much below normal temperatures for
mid-March will further assist in causing periods of heavy snow for
the Wasatch, Teton, Wind River, Bighorn, Park, and Laramie Ranges.
WPC probabilities for snowfall >8" on Day 2 are up to 50% in these
ranges with the Wasatch featuring slightly higher probabilities

70% chance). The trough continues to amplify as a trailing

vorticity maximum dives south into the Southwest on Day 3. Heavy
snowfall may occur as far south and west as the Mogollon Rim in
northern Arizona, but the best chances for snow totals >8" reside
in southwest CO. More specifically, the San Juans have a moderate
chances (>50%) for snowfall totals >8" through Day 3. In total
across all three days, the higher mountains ranges of Wyoming,
Utah, and the Colorado Rockies could end up with 1 to 2 feet of
snow by Thursday evening. Heavy snowfall rates and gusty winds may
result in near-whiteout conditions and make for treacherous travel
conditions.

...Central Plains...
Days 2-3...
As the upper trough in the West continues to amplify and dig
southeast, a wave of low pressure will strengthen in lee of the
central Rockies Wednesday afternoon. A tightening 850-700mb front
and diffluent flow in the left exit region of a jet streak over
the Four Corners region will result in banded areas of snow,
falling heavily at times Wednesday afternoon and into Wednesday
night. By Thursday, periods of snow will blanket parts of the
central Plains and Midwest but diminishing upper level support
should lead to diminishing snowfall rates by the time the shield
of snow reaches the Mississippi River. Latest guidance has come in
with slightly colder temperatures aloft but deterministic guidance
continue to show differences in placement of where the heaviest
banding of snow sets up. Latest WPC probabilities indicate as high
as a 60-70% chance for snow totals >6" in southwest Nebraska.
Chances for snow totals of 6" or more are as high as 50% from
southeast Wyoming and across southern Nebraska. There are
solutions that depict snowfall amounts as high as a foot in parts
of southwest Nebraska and it is still possible for higher snowfall
totals in the 8-12" range to expand should guidance come into
better consensus on where the deformation zone sets up in the
coming days.

Mullinax

$$




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FOUS11 KWBC 080838
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
337 AM EST Tue Mar 08 2022

Valid 12Z Tue Mar 08 2022 - 12Z Fri Mar 11 2022

...Western U.S....
Days 1-3...
A series of shortwaves diving south through western Canada will
amplify the upper pattern over the Northwest beginning with a wave
dropping into the region later this morning. This will be
followed a more defined shortwave digging into the Northwest
Tuesday night. Favorable forcing aloft will support snow
developing along a strong surface-to-low level baroclinic zone as
it pushes south through the Northwest and northern Rockies on
Tuesday. As the upper shortwave continues to amplify and dig
southeast, the front is expected to push into the Great Basin and
central Rockies on Wednesday, and eventually through the Southwest
and southern Rockies on Thursday. Mountain snows of 4-8 inches
will likely be common, with locally heavier amounts expected, from
the Washington and Oregon Cascades southeastward to the central
Rockies. WPC probabilities show the greater potential for locally
heavier amounts of a foot or more centering across the Tetons and
Wasatch into the western Colorado ranges. Models show the front
lingering across the region ahead of the approaching shortwave,
with ample moisture and upper forcing helping to support heavy
accumulations.

...Central Rockies to Mid Mississippi Valley...
Days 2-3...
Upslope flow behind the front pushing south trough the Rockies and
High Plains will support snow developing and spreading south along
the central and eastern Wyoming ranges on Tuesday. The better
potential for organized heavier snow is expected to settle into
southern Wyoming overnight. A low level wave dropping southeast
across the state is expected to enhance the upslope flow into the
southeastern Wyoming ranges, raising the potential heavy amounts
along the Laramie, Medicine Bow, and Sierra Madre mountains.

Meanwhile as the low level wave drops through the High Plains this
is expected to increase theta-e advection into the boundary over
the Plains. This along with increasing upper divergence afforded
by a coupled upper jet is expected to support snow spreading east
across southern Nebraska and northern Kansas. The overnight model
consensus has shifted south, but still shows a good signal for at
least light to moderate snows developing across the region.
Latest WPC probabilities indicate that accumulations of 4 inches
or more are likely from far northeastern Colorado across
southwestern Nebraska and northwestern Kansas, with a significant
threat for accumulations of 8 inches or more over northwestern
Kansas.

As the upper trough begins to move east of the Rockies, snow is
expected to spread farther east ahead of a low level wave tracking
northeast from northern Oklahoma through southeastern Kansas
Thursday. This is expected to bring at least light to moderate
snows from northeastern Kansas and southeastern Nebraska through
northern Missouri and southern Iowa.

...Northeast & Mid Atlantic...
Days 1-2...
A well-defined shortwave moving across the southern Rockies this
morning is forecast to move steadily northeast, reaching the
Northeast by late tomorrow. Consensus of the overnight guidance
has trended wetter across portions of the northern Mid Atlantic
into southern New England. Meanwhile, thermal profiles appear
sufficient for snow at least at the onset as precipitation spreads
northeast from the central Appalachians and interior Mid Atlantic
into the Northeast on Wednesday. With the overnight trends,
probabilities for at least a couple of inches of snow have
increased from West Virginia into northern Pennsylvania along the
Allegheny Mountains and eastward into the Poconos and Catskills.
Probabilities have also increased farther east along the
Berkshires and Worcester Hills.

Pereira

$$




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FOUS11 KWBC 090852
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
351 AM EST Wed Mar 09 2022

Valid 12Z Wed Mar 09 2022 - 12Z Sat Mar 12 2022

...Northern Mid Atlantic and Northeast...
Day 1...
Precipitation associated with a fast-moving mid level shortwave
will continue to spread north through the Mid Atlantic this
morning and into the Northeast by early afternoon. Reflecting the
warm current temperatures, guidance has been shifting the southern
edge of accumulating snows farther to the north. However there is
still significant potential for at least a couple of inches of
snow, especially on grassy surfaces, across portions of the
interior northern Mid Atlantic and the Northeast. WPC
probabilities have decreased some, but still remain high for
accumulations of 2 inches or more across portions of the Northern
Tier of Pennsylvania and Southern Tier of New York into the
Poconos, Catskills, and Berkshires, with a slight chance (10-30
percent) for amounts of 4 inches or more across those areas.

...Western U.S., including the central and southern Rockies...
Days 1-3...
A shortwave dropping south into the Pacific Northwest this morning
will continue to amplify and dig south across the region, driving
a strong baroclinic zone farther south across the Great Basin and
central Rockies today into early tomorrow. Overall, expecting
mostly light accumulations over the next 24 hours across the
higher elevations of the Great Basin into the central Rockies.
However, locally heavy accumulations of 8 inches or more are
possible, especially along the southern Wasatch and the western
Colorado ranges. East of the Divide, upslope flow on the backside
of a low level wave dropping south across eastern Colorado will
support snow spreading south along the Front Range and adjacent
High Plains. WPC probabilities show accumulations of 4-8 inches
likely, with locally heavier amounts possible along the Front
Range and southern Medicine Bow Mountains today.

On Thursday, the low in the High Plains is forecast to drop
southeast across the Texas Panhandle into western Oklahoma, with
the trailing boundary pushing south through eastern New Mexico.
Upslope flow/low level convergence, coupled with favorable upper
jet forcing, is expected to support the potential for heavy snow
along the Sangre de Cristo and San Juan mountains. WPC
probabilities indicate that accumulations of 4-8 inches are
likely, with significant potential for locally heavier amounts,
especially along the Sangre de Cristo Mountains. Meanwhile
farther to the west, the previously noted upper shortwave digging
through the western U.S. is forecast to drop into the Southwest,
bringing at least light snows into the higher elevations of
northern and central Arizona on Thursday.

As the upper trough pivots east, some generally light snows are
expected to spread south into southern New Mexico and far western
Texas before the trough moves east of the region and surface high
pressure settles in late Friday.

...Central Plains to the Mid Mississippi Valley...
Days 1-2...
There remains a good signal for at least light to moderate and
potentially heavy snows developing over far northeastern Colorado
and spreading east across southwestern Nebraska and northwestern
Kansas beginning later today and continuing through the overnight.
Deepening moisture along a low-to-mid level front, along with
favorable upper jet forcing, is expected to support the
development of snow across this region. Probabilities have
shifted slightly south from the daytime run, but still indicate
that by early Thursday accumulations of 4-8 inches are likely
along an west-east axis extending from northeastern Colorado along
the western Nebraska and Kansas border. WPC probabilities still
show a slight chance (10-30 percent) for accumulations of 8 inches
or more across a small portion of southwestern Nebraska and
northwestern Kansas.

This initial band is forecast to shift east across eastern Kansas
into northern Missouri and southern Iowa Thursday morning into the
afternoon before weakening, with generally light snow spreading
northeast into the western Great Lakes during the evening and
overnight. However, southerly flow into a lingering low level
boundary is expected to support redeveloping snows over Kansas,
then shifting south along the with the boundary into northern
Oklahoma and the Texas Panhandle Thursday night and Friday morning.

...Southern Plains to the Northeast...
Day 3...
On Friday, the southern stream shortwave moving out the southern
Rockies will begin to phase with a northern stream trough
amplifying over the Midwest. Ahead of of the southern stream
wave, generally light to moderate snow is expected to spread east
from Oklahoma and northern Texas through southern Missouri and
northern Arkansas, into the Mid South and lower Ohio Valley along
a low-to-mid level frontal band. By Friday evening, surface low
pressure is forecast to quickly develop and track northeast from
the central Gulf Coast region into the Carolinas by Saturday
morning. Snow is expected to develop west of the low and along a
strong low-to-mid level front pushing east across the Ohio Valley
and eastern Great Lakes Friday night and Saturday morning. For
the 24 hour period ending Saturday morning, WPC probabilities
indicate a moderate chance (40 percent) chance for snow
accumulations of 4 inches extending from portions of eastern
Tennessee and Kentucky to the Lower Great Lakes region.

Pereira








$$




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FOUS11 KWBC 100838
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
337 AM EST Thu Mar 10 2022

Valid 12Z Thu Mar 10 2022 - 12Z Sun Mar 13 2022

...Southern Rockies to Central Plains...
Day 1...

Shortwave trough energy dropping through the Intermountain West
this morning will reach the Four Corners region by 12Z Friday. A
pair of surface fronts slowly moving through the region as well
combined with the impressive height falls and large scale forcing
for ascent will continue the widespread moderate to locally heavy
precipitation today. The bulk of the heaviest snow amounts will be
across the favored terrain areas where WPC probabilities for 4
inches are moderate to high, particularly for the San Juans Ahead
of it, height falls and upper divergence will bring a large area
of forcing for ascent. This will bring an area of moderate to
locally heavy precipitation for the San Juans and Sangre De
Cristos.

Across the Central Plains this morning, a zone of mid-level
frontogenesis and an inverted trough across Kansas will continue
to support a corridor of moderate to locally heavy snowfall
through mid-day. Additional accumulations will be focused on
eastern KS to western MO where upwards of 2-4" are expected.

...Pacific Northwest...
Day 3...
A compact shortwave trough closing off over northwest Washington
late on D3 will push a narrow plume of moisture into the region.
IVT values approach moderate levels and the forcing for ascent
combined with upslope flow supports widespread precipitation
during the back half of the period. Snow levels generally
3000-6000+ ft will confine the greatest snow accumulations to the
higher peaks and the latest WPC probabilities are high for 4"
across the WA Olympics and Cascades with a slight to moderate
signal for 8-12"+ totals.

...Ohio Valley to Mid-Atlantic and Northeast...
Days 2-3..

A pair of shortwave troughs within the northern and southern
streams will approach the central U.S. Friday into Friday night
and intensify early Saturday as phasing commences. The combined
trough axis then takes on a strong neutral tilt Saturday into
Saturday night leading to impressive forcing for ascent
downstream. Strong mid to upper divergence and a coupled jet
streak over the East Coast will help deepen a surface low
originating from the Southeast as it moves through the
Mid-Atlantic and eastern New England. Strong CAA on the backside
of the deepening low will result in a changeover from rain to snow
and just to the northwest/north of the low center, a corridor of
heavy snow is likely. Within this snow band, snow rates are likely
to be 1-2"/hr and this will likely overcome any warm ground
temperatures at its peak. With upwards of 0.75 to 1.5" of QPF,
significant snow accumulations are possible, particularly for the
interior Northeast.

WPC probabilities for D2 are moderate (40-50%) for TN and reach
above 60 percent for much of central/eastern KY northeast through
eastern OH, western WV toward western NY. Into the terrain of
Upstate New York and Northern New England, this event is likely to
be all snow, and will be heavy at times. WPC probabilities are
above 90% for 4 inches, as high as 50-60% for 12+ inches in the
Adirondacks. An impactful swath of double-digit snow totals is
likely across much of the interior Northeast.

Taylor


~~~ Key Messages for Tennessee Valley through the Northeast Winter
Storm ~~~

-Confidence continues to increase in a significant and impactful
winter storm for portions of Tennessee and Ohio Valleys through
the interior Eastern U.S. late Friday through Saturday.

-Snow rates greater than 1rC/hr, gusty winds, and severely
reduced visibility will make for hazardous to difficult driving
conditions and travel at times, particularly across the interior
Northeast.

-The greatest accumulations are likely across portions of the
interior Northeast where totals in excess of 12rC are likely.

-In the wake of the storm system, much colder air will spread
across the Southeast and Mid-Atlantic with lows likely below
freezing along the Gulf Coast and northern Florida Sunday morning.










$$




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FOUS11 KWBC 102018
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
318 PM EST Thu Mar 10 2022

Valid 00Z Fri Mar 11 2022 - 00Z Mon Mar 14 2022

...Southern Rockies...
Day 1...

A potent shortwave will continue to advect southward across the
Four Corners before weakening and ejecting into the westerlies
across the Southern Plains. This will spread moderate to heavy
snowfall into the region, and although the heaviest snow is likely
above 2000 ft, snow levels to the surface should produce heavy
snow out into the High Plains as well. Upslope flow behind a cold
front will continually enhance snowfall on the eastern slopes of
the terrain and into the Raton Mesa through early Friday. There is
a chance for a band of heavy snowfall to develop near the terrain
and shift eastward in response to enhanced fgen and a deepening
DGZ which could exceed 100mb, and a narrow corridor of 1"/hr or
greater snowfall is likely in the greatest upslope flow but also
within this west to east moving band. WPC probabilities are high
for more than 4 inches of snow in the Sangre De Cristos, the
Sacramentos, and along the Raton Mesa D1, with locally in excess
of 8 inches possible.


...Pacific Northwest...
Day 3...

A potent closed low dropping out of the Gulf of Alaska will
approach the Pacific Northwest coast Saturday night and lift
onshore as far east as the Northern Rockies while filling on
Sunday. This feature will be accompanied by a robust Pacific jet
streak and WAA ahead of a cold front which will help spread
moisture onshore while snow levels rise to 3000-5000 ft. Above
these levels, heavy snow is likely as the shortwave advects
eastward enhancing deep layer ascent which will be aided by
upslope flow as mid-level winds nearly orthogonally intersect some
of the terrain. WPC probabilities for more than 6 inches of
snowfall are high in the Olympics and both WA and OR Cascades,
with lesser accumulations likely into the Sawtooth Range and
Northern Rockies. Light to moderate snowfall accumulations are
likely at the Cascade Passes across WA and OR on Sunday.


...Upper Midwest...
Days 1-2...

A modest clipper type low will drive an arctic front southeast
from Canada tonight, moving into MN by Friday morning, and then
across Michigan later Friday. While moisture ahead of this front
is modest, intense ascent along the front could produce clusters
of heavy snow showers or snow squalls. The snow squall parameter
reaches 3 over eastern ND and northwest MD tonight, with a
secondary increase Friday aftn/eve in eastern WI and across the
L.P. of MI. Impressive 0-2km fgen along the front and steepening
0-2km theta-e lapse rates are supportive of intense snow squalls,
but instability is somewhat limited. Still, at least heavy snow
showers seem likely, and if instability can become a bit more
impressive, snow squalls with extremely limited visibility and
gusty winds are possible despite overall light accumulations
expected.


...Mid-Mississippi Valley through the Mid-Atlantic and Northeast...
Days 1-3..

A surface cold front will stall as a stationary front across the
Mid-South/TN Vly late Friday while a secondary arctic front
approaches from the NW. Along the lead front, a southern stream
shortwave moving out of the Desert Southwest will shift eastward
while weakening, but will likely interact/phase with a northern
stream shortwave digging out of Alberta to form a neutrally tilted
longwave trough near the Ohio Valley. At the same time, downstream
jet streaks will intensify to near or above record strength
according to the SPC sounding climatology, and form an impressive
coupled jet structure lifting northeast across the eastern CONUS.
While there remains some spread in the location and intensity of
this overlap of features,it is likely a surface low will develop
near the Gulf Coast and then move relatively quickly northeast
while explosively deepening. Northwest of this track, heavy snow
is likely.

On D1, the highest WPC probabilities for more than 4 inches of
snow are confined to the Ozarks of Missouri and Arkansas, and
reach as high as 30%. This is where an overlap of isentropic
ascent from the Gulf of Mexico leads to higher moisture, and is
acted upon by the overlap of elevated fgen and the LFQ of a
subtropical jet streak. However, more significant snow develops D2
as the surface low begins to deepen and eject northeastward, and
the coupled jet structure strengthens downstream of the phasing
longwave trough. An expanding area of precipitation will likely
spread from the southern Tennessee Valley as far north as northern
New England as WAA increases. Initially, the column will be too
warm for snow except in northern New England and the far NW
portion of the TN and OH VLY. However, rapid CAA will quickly cool
the column, while at the same time leading to tightening fgen
overlapping the strengthening deformation axis. This will cause
rain to change quickly to snow from west to east, and snowfall
will likely become heavy within a narrow band from central TN
through eastern KY and up tin WV, PA, and Upstate NY. The guidance
is in good agreement in this band occurring, and some of the
models suggest folded theta-e collocated with -EPV favorable for
CSI or even upright convection, and snowfall rates reaching 2"/hr.
This convective snowfall could quickly overcome the hostile
antecedent conditions, and WPC probabilities for more than 4
inches have increase to more than 10% as far south as Huntsville,
AL, and above 50% from eastern TN through western MD and into much
of northern New England. More than 12 inches of snow is likely in
Upstate NY and northern New England where most of the event should
be cold enough for heavy snow. By D3, this low quickly pulls away
to the northeast while continuing to deepen into Canada, and
residual heavy snow will linger into Maine and far northern NH/VT
early D3 before pivoting off to the northeast. WPC probabilities
for 4+ inches are high in Canada D3, and storm total snowfall may
reach 18 inches in parts of the Adirondacks and northern New
England.

Along the I-95 corridor from Washington, D.C. to Boston, MA,
snowfall is likely to be much less. However, the guidance this
aftn has trended a bit more progressive and colder. This colder
solution combined with the impressive CAA/fgen that will cause a
rapid transition from rain to snow has led to an increase in
snowfall probabilities on Saturday for the urban areas of the
Northeast. Heavy snow rates which could reach 1"/hr will likely
overwhelm antecedent warm/rain, and WPC probabilities for at least
1 inch of snow is as high as 70% for the I-95 corridor from
Washington, D.C. to NYC, with slightly lower probabilities into
Boston, MA.


Weiss

~~~ Key Messages for the Tennessee Valley through Northeast Winter
Storm ~~~

- A significant and impactful winter storm is likely for portions
of the Tennessee and Ohio Valleys, through the interior Eastern
United States late Friday through Saturday.

- Snow rates of greater than 1"/hr combined with gusty winds will
produce blowing and drifting of snow and severely reduced
visibility. This will create difficult to hazardous travel
conditions.

- The greatest snow accumulations are likely across portions of
the interior Northeast where totals in excess of 12 inches are
likely. This could lead to scattered power outages due to the
heavy and wet nature of the snowfall.

- In the wake of the storm system, much colder air will spread
across the Southeast and Mid-Atlantic with lows likely below
freezing along the Gulf Coast and northern Florida Sunday morning.




$$




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FOUS11 KWBC 110912
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
411 AM EST Fri Mar 11 2022

Valid 12Z Fri Mar 11 2022 - 12Z Mon Mar 14 2022

...Mid-Mississippi Valley through the Mid-Atlantic and Northeast...
Days 1-2...

A surface cold front will stall as a stationary front across the
Mid-South/TN Valley late Friday while a secondary arctic front
approaches from the NW. Along the lead front, a southern stream
shortwave moving out of the Desert Southwest will shift eastward
while weakening, but will likely interact/phase with a northern
stream shortwave digging out of Alberta to form a neutrally tilted
longwave trough near the Ohio Valley. At the same time, downstream
jet streaks will intensify to near or above record strength
according to the SPC sounding climatology, and form an impressive
coupled jet structure lifting northeast across the eastern CONUS.
Spread in the location and intensity of this overlap of features
is decreasing, and it is likely a surface low will develop near
the Gulf Coast and then move relatively quickly northeast while
explosively deepening. Northwest of this track, heavy snow is
likely.

On D1, as the surface low begins to deepen and eject northeastward
with the coupled jet structure strengthening downstream of the
phasing longwave trough, an expanding area of precipitation will
likely spread from the southern Tennessee Valley as far north as
northern New England as WAA increases. Initially, the column will
be too warm for snow except in northern New England and the far NW
portion of the TN and OH Valley. However, rapid CAA will quickly
cool the column, while at the same time leading to tightening fgen
overlapping the strengthening deformation axis. This will cause
rain to change quickly to snow from west to east, and snowfall
will likely become heavy within a narrow band from central TN
through eastern KY and farther north into WV, PA, and Upstate NY.
The guidance is in good agreement in this band occurring, and some
of the models suggest folded theta-e collocated with -EPV
favorable for CSI or even upright convection, and snowfall rates
reaching 2"/hr. This convective snowfall could quickly overcome
the hostile antecedent conditions, and WPC probabilities for more
than 4 inches are as high as 10% as far south as Huntsville, AL,
and above 50% from eastern TN through western MD and into much of
Upstate NY and northern New England. More than 8 inches of snow is
likely in Upstate NY and northern New England where most of the
event should be cold enough for heavy snow, and more than 12
inches is likely across portions of the Green and White Mountains
where upslope flow is maximized. By D2, this low quickly pulls
away to the northeast while continuing to deepen into Canada, and
residual heavy snow will linger into Maine and far northern NH/VT
early D2 before pivoting off to the northeast. WPC probabilities
for 8+ inches are high in Canada D2, and storm total snowfall may
reach 18 inches in parts of the Adirondacks and northern New
England.

Along the I-95 corridor from Washington, D.C. to Boston, MA,
snowfall is likely to be much less. However, the guidance
overnight has continued to trend a bit more progressive and
colder. This colder solution combined with the impressive CAA/fgen
that will cause a rapid transition from rain to snow has led to a
continued increase in snowfall probabilities on Saturday for the
urban areas of the Northeast. Heavy snow rates which could reach
1"/hr will likely overwhelm antecedent warm/rain, and WPC
probabilities for at least 1 inch of snow are as high as 70% for
the I-95 corridor from Washington, D.C. to NYC, with slightly
lower probabilities into Boston, MA. Along that same stretch from
D.C. to NYC the WPC probabilities for 4+ inches have increased to
5-10%, while just west of I-95 those probabilities are as high as
20-30%.


...Pacific Northwest...
Days 2-3...

A potent closed low dropping out of the Gulf of Alaska will
approach the Pacific Northwest coast Saturday night and lift
onshore as far east as the Northern Rockies while filling on
Sunday. This feature will be accompanied by a robust Pacific jet
streak and WAA ahead of a cold front which will help spread
moisture onshore while snow levels rise to 3000-5000 ft. Above
these levels, heavy snow is likely as the shortwave advects
eastward enhancing deep layer ascent which will be aided by
upslope flow as mid-level winds nearly orthogonally intersect some
of the terrain. WPC probabilities for more than 6 inches of
snowfall are high in the Olympics and both WA and OR Cascades,
with lesser accumulations likely into the Sawtooth Range and
Northern Rockies. Light to moderate snowfall accumulations are
likely at the Cascade Passes across WA and OR on Sunday.


Weiss/Churchill


~~~ Key Messages for the Tennessee Valley through Northeast Winter
Storm ~~~

- A significant and impactful winter storm is likely for portions
of the Tennessee and Ohio Valleys, through the interior Eastern
United States late tonight through Saturday.

- Snow rates of greater than 1"/hr combined with gusty winds will
produce blowing and drifting of snow and severely reduced
visibility. This will create difficult to hazardous travel
conditions.

- The greatest snow accumulations are likely across portions of
the interior Northeast where totals in excess of 8 inches are
likely. This could lead to scattered power outages due to the
heavy and wet nature of the snowfall.

- In the wake of the storm system, much colder air will spread
across the Southeast and Mid-Atlantic with lows likely below
freezing along the Gulf Coast and northern Florida Sunday morning.




$$




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FOUS11 KWBC 111955
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
254 PM EST Fri Mar 11 2022

Valid 00Z Sat Mar 12 2022 - 00Z Tue Mar 15 2022

...Mid-Mississippi Valley, Ohio Valley, Mid-Atlantic, and
Northeast...
Days 1-2...

A rapidly deepening surface low will eject from near the Gulf
Coast, through the Mid-Atlantic, and up across New England tonight
through Sunday morning. This low will strengthen in response to
impressive height falls ahead of a longwave trough which will
amplify in response to shortwave phasing of the southern and
northern streams. As this trough sharpens across the OH VLY and
shifts eastward, extremely impressive jet streak coupling will
occur as the LFQ of a subtropical jet streak with near record
intensity according to SPC sounding climatology couples with the
RRQ of departing northern stream jet energy moving into Canada.
The overlap of the jet streaks with the height falls above an
intensifying baroclinic zone along a surface cold front will drive
explosive cyclogenesis, and this low is likely to bomb as it moves
into Maine/Canada. Robust WAA will drive increasing moisture from
the southern Appalachians into New England, which will help expand
the precipitation shield and yield to a large swath of heavy snow
from northern MS through northern New England. Within this swath
of heavy snow, a pronounced and intensifying band of fgen is
likely in response to strong CAA on gusty NW winds, and within
this band there are signals for CSI or potentially upright
convection /thunder snow/ as far south as TN. Where this band
translates from SW to NE, snowfall rates will likely reach 2"/hr
as shown by HREF and NBM probabilities, with the greatest snowfall
rates likely from TN through eastern KY, with a second maxima
possible in VT/NH/ME. Additionally, this strengthening fgen
combined with a slightly further east track which appeared in the
guidance at 12Z today suggests the rain/snow line will collapse
more rapidly eastward, and this has led to an increase in snowfall
for I-95 and points east. Here, the precipitation will initially
be rain but will likely change over to a brief period of sleet and
then quickly heavy snow with rates of 1"/hr or greater, which
should overwhelm the antecedent hostile conditions to rapidly
accumulate. While amounts are likely to be much less for the urban
corridor, impacts could still be substantial. The entire system
will pull away quickly Sunday morning with lingering moderate to
heavy snow across Maine Sunday before exiting to the northeast
thereafter.

WPC probabilities for heavy snow on D1 are above 50% for 6+ inches
in NE TN, eastern KY, and the higher terrain of WV, where locally
8-10" is possible. A secondary max of snow is likely from
northeast PA into Upstate NY and much of northern New England
where WPC probabilities are above 60% for 6+ inches and locally 12
inches is likely in the higher terrain of VT/NH and ME. The PWPF
does not account for melting at snowfall onset, especially for the
I-95 corridor, so may be a bit overdone, but the impressive rates
should still lead to several inches of snowfall on Saturday, and
WPC probabilities for 2+ inches are above 70% for Washington, D.C.
to Philadelphia, and above 50% for NYC, but lower for Boston. By
D2 the heavy snow will be confined to far northern Maine.

Behind the system, a pronounced cold pool aloft within the
impressive trough will increase instability across the Great Lakes
and Ohio Valley. The high-res guidance is in good agreement that
afternoon snow showers and snow squalls will develop and advect
southeast through the evening, potentially reaching the Central
Appalachians later Saturday evening. Although snowfall
accumulation will be light, intense snowfall rates of more than
1"/hr and gusty winds will likely produce widespread periods of
severely limited visibility and difficult travel.


...Pacific Northwest...
Days 2-3...

A potent closed low will drop out of the Gulf of Alaska and then
move onshore the Pacific Northwest coast Saturday night while
slowly filling. This feature will open into a positively tilted
trough and advect through the Northern Rockies and then flatten
into the Northern Plains by Sunday night. This feature will
combine with weakly coupled jet streaks as a the RRQ of a
departing jet streak shifts eastward and a Pacific jet streak
moves into CA. The overlap of these height falls with the upper
coupled jets will provide ascent into a modestly moistening column
to produce moderate to heavy snow in the terrain of the Northwest.
D2 WPC probabilities are high for 6+ inches in the Olympics and
WA/OR Cascades, with lesser probabilities into the Sawtooth and
Northern Rockies. By D3 the primary trough shifts eastward, but
residual jet-level ascent will continue to produce moderate snow
in the WA Cascades. Light to moderate snowfall accumulations are
likely at the Cascade Passes across WA and OR on Sunday.


Weiss


~~~ Key Messages for the Tennessee Valley through Northeast Winter
Storm ~~~

- A significant winter storm is likely for portions of the
Tennessee and Ohio Valleys, northeastward into the Mid-Atlantic
and New England tonight through early Sunday.

- Snow rates of 1-2"/hr combined with strong and gusty winds up to
50 mph will produce blowing and drifting snow even after the snow
ends. Severely reduced visibility and white-out conditions will
make travel extremely dangerous at times.

- Snow accumulations of 6-12+ inches are likely over much of the
interior Northeast. Up to several inches are possible closer to
the coast which will fall quickly Saturday morning.

- Strong winds and the heavy wet snow could lead to scattered
power outages and tree damage. Untreated surfaces will freeze over
as temperatures drop sharply.

- Record cold is likely for much of the Southeast Sunday morning
as temperatures fall below freezing along the Gulf Coast and
through northern Florida.

$$




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FOUS11 KWBC 120821
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
320 AM EST Sat Mar 12 2022

Valid 12Z Sat Mar 12 2022 - 12Z Tue Mar 15 2022

...Mid-Atlantic and Northeast...
Day 1...

Low pressure over central Georgia this morning will rapidly deepen
as it tracks toward the Mid-Atlantic and across eastern New
England today, bottoming out just under 970 mb later this evening
near Nova Scotia. This quick deepening is driven by impressive
height falls associated with an approaching mid level trough axis
currently sweeping through the mid-MS to lower OH Valley and also
a strengthening coupled jet streak. The overlap of the jet streaks
with the height falls above an intensifying baroclinic zone along
a surface cold front will help bomb out the cyclone. The
increasing moisture and warm air advection will bring a shield of
precipitation northward up the eastern U.S. while the Arctic air
mass pours southeast behind the cold front. As the cyclone
deepens, impressive cold air advection will lead to a rapid
transition and changeover from rain to wet, heavy snow along and
northwest of the low center where the frontogenesis banding is
most pronounced. Within this narrow deformation band, snow rates
1-2"/hr are expected as shown by the latest HREF with the greatest
snowfall rates early this morning across the TN to
southern/central Appalachians then reaching the Mid-Atlantic and
Northeast later this morning and New England this
afternoon/evening. The trend this cycle has been for a slightly
wetter solution and a nudge to the south/east with the axis of
heaviest precipitation, which minor increases in snow amounts
along and just west of the I-95 corridor. The greatest snow totals
for the D1 period are still favored for interior Northeast
locations where the latest probabilities for 6"+ remain above 50
percent and well above 80 percent for interior New England. Along
the I-95 urban corridor, a difficult/challenging forecast as
melting at the onset and the rapidly evolving precipitation
changeover difficult to pinpoint but potential exists for a very
intense 2-4 hour period where snow rates will be high enough to
overcome any warm ground temperatures and combined with the gusty
winds, difficult to dangerous impacts may still occur.

As the core of the mid/upper level trough swings through the Great
Lakes and Ohio Valley during the afternoon/evening, steepening low
level lapse rates during the diurnal maximum will likely bring
scattered to numerous snow showers and snow squalls as far
southeast as the Central Appalachians. Gusty winds and snow rates
up to 1"/hr will be possible and this could create difficult to
hazardous conditions including severely limited visibility.

...Pacific Northwest...
Days 1-3...

A compact, potent closed low reaches the Pacific Northwest late
tonight into Sunday afternoon before filling as it moves inland.
The system then takes on a positive to neutral tilt as it crosses
the northern Rockies. Combined with favorable upper jet dynamics,
orographic lift and a favorable, modest atmospheric river,
widespread precipitation is expected with heavy snow confined to
the terrain areas of the Olympics and Cascades where WPC
probabilities remain high for 6+ inches. Lesser probabilities for
significant snow exist for the Sawtooth and Northern Rockies.

Another system reaches the region late on D3 as a fast moving
shortwave energy rounds the base of a closed low near the Gulf of
Alaska. This opens up into a large scale trough as it swings
onshore. Modest moisture combined with the favorable height falls
and lift will produce widespread precipitation late Monday into
Tuesday. This system is a bit warmer with higher snow levels so
the greater probabilities for significant snowfall are confined to
the higher elevations of the northern WA Cascades. There, WPC
probabilities for 6 inches are more reach moderate to high
percentages.


Taylor


~~~ Key Messages for the Tennessee Valley through Northeast Winter
Storm ~~~

-Snow rates of 1-2"/hr combined with wind gusts up to 50 mph will
produce blowing and drifting snow at times this morning from the
Central Appalachians to Mid-Atlantic and then the Northeast later
this morning through the late afternoon. Severely reduced
visibility and white-out conditions will make travel extremely
dangerous at times.

-Snow accumulations of 6-12"+ are expected over much of the
interior Northeast. Closer to the coast and I-95 corridor, a burst
of intense snowfall may accumulate up to a few inches in a very
short period.

-Strong winds and the heavy wet snow could lead to scattered power
outages and tree damage. Untreated surfaces will freeze over as
temperatures drop sharply.

-Record cold is likely for much of the Southeast Sunday morning as
temperatures fall below freezing along the Gulf Coast and through
northern Florida.


$$




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FOUS11 KWBC 122017
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
316 PM EST Sat Mar 12 2022

Valid 00Z Sun Mar 13 2022 - 00Z Wed Mar 16 2022

...Northeast..
Day 1...

A strong low pressure system will continue to deepen as it lifts
away from New England and into the Canadian Maritimes. A residual
deformation band will pivot across northern Maine tonight before
ending from SW to NE by Sunday morning. As this low pulls away,
drier air will advect in from the west bringing an end to most of
the snowfall. However, intense NW flow and CAA beneath a deep
longwave trough will produce, upslope snow into the terrain of
upstate NY and Northern New England, light LES off Lake Ontario,
and modest snow showers within the instability pool through early
Sunday. Most of this snowfall should be light, but WPC
probabilities for at least 4 inches of snow are 10-30% across
northern Maine, the White Mountains of NH, and the Northeast
Kingdom of VT.


...Upper Midwest...
Day 2...

A potent jet streak racing west to east across the Northern Plains
and Upper Midwest will drive ascent atop an elevated baroclinic
gradient north of a cold front sinking into the Mid-MS VLY. A weak
wave of low pressure along this front will shift southeast,
driving subtly enhanced warm advection which will isentropically
ascend the Canadian high to produce an expanding precipitation
shield from North Dakota through the western Great Lakes. The most
robust overlap of forcing and moisture is likely from eastern MN
through the U.P. and northern L.P. of MI, where some enhanced fgen
is likely to drive heavier snow rates. This feature will move
quickly eastward, but WPC probabilities for more than 4 inches are
as high as 10% in a narrow corridor from WI through MI.


...Pacific Northwest...
Days 1-3...

Two distinct shortwaves will move onshore Washington State during
the next three days, each one accompanied by Pacific jet energy
and a surface cold front. The combination of the upper jet and WAA
ahead of the surface front will increase moisture into the region,
upon which the deep layer ascent will produce snowfall in the
terrain of the region. Each shortwave is potent and compact, but
also fast moving as the mid-level flow remains pinched. Shortwave
ridging between the two features will reduce snowfall on D2, but
heavy snow is likely both D1 and D3. For D1, WPC probabilities are
high for 6+ inches in the OR Cascades, with moderate probabilities
extending into the Blue Mountains, the Sawtooth, parts of the
Northern Rockies, the Tetons, and the Wind Rivers. The second
impulse will be displaced a but further north than the lead
shortwave, and WPC probabilities for more than 6 inches are high
in the WA Cascades and Olympics, with moderate probabilities
extending into the Northern Rockies.


Weiss


~~~ Key Messages for the Tennessee Valley through Northeast Winter
Storm ~~~

-Snow rates of 1-2"/hr combined with wind gusts up to 50 mph will
produce blowing and drifting snow at times this morning from the
Central Appalachians to Mid-Atlantic and then the Northeast later
this morning through the late afternoon. Severely reduced
visibility and white-out conditions will make travel extremely
dangerous at times.

-Snow accumulations of 6-12"+ are expected over much of the
interior Northeast. Closer to the coast and I-95 corridor, a burst
of intense snowfall may accumulate up to a few inches in a very
short period.

-Strong winds and the heavy wet snow could lead to scattered power
outages and tree damage. Untreated surfaces will freeze over as
temperatures drop sharply.

-Record cold is likely for much of the Southeast Sunday morning as
temperatures fall below freezing along the Gulf Coast and through
northern Florida.


$$




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FOUS11 KWBC 122059
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
358 PM EST Sat Mar 12 2022

Valid 00Z Sun Mar 13 2022 - 00Z Wed Mar 16 2022

...Northeast..
Day 1...

A strong low pressure system will continue to deepen as it lifts
away from New England and into the Canadian Maritimes. A residual
deformation band will pivot across northern Maine tonight before
ending from SW to NE by Sunday morning. As this low pulls away,
drier air will advect in from the west bringing an end to most of
the snowfall. However, intense NW flow and CAA beneath a deep
longwave trough will produce, upslope snow into the terrain of
upstate NY and Northern New England, light LES off Lake Ontario,
and modest snow showers within the instability pool through early
Sunday. Most of this snowfall should be light, but WPC
probabilities for at least 4 inches of snow are 10-30% across
northern Maine, the White Mountains of NH, and the Northeast
Kingdom of VT.


...Upper Midwest...
Day 2...

A potent jet streak racing west to east across the Northern Plains
and Upper Midwest will drive ascent atop an elevated baroclinic
gradient north of a cold front sinking into the Mid-MS VLY. A weak
wave of low pressure along this front will shift southeast,
driving subtly enhanced warm advection which will isentropically
ascend the Canadian high to produce an expanding precipitation
shield from North Dakota through the western Great Lakes. The most
robust overlap of forcing and moisture is likely from eastern MN
through the U.P. and northern L.P. of MI, where some enhanced fgen
is likely to drive heavier snow rates. This feature will move
quickly eastward, but WPC probabilities for more than 4 inches are
as high as 10% in a narrow corridor from WI through MI.


...Pacific Northwest...
Days 1-3...

Two distinct shortwaves will move onshore Washington State during
the next three days, each one accompanied by Pacific jet energy
and a surface cold front. The combination of the upper jet and WAA
ahead of the surface front will increase moisture into the region,
upon which the deep layer ascent will produce snowfall in the
terrain of the region. Each shortwave is potent and compact, but
also fast moving as the mid-level flow remains pinched. Shortwave
ridging between the two features will reduce snowfall on D2, but
heavy snow is likely both D1 and D3. For D1, WPC probabilities are
high for 6+ inches in the OR Cascades, with moderate probabilities
extending into the Blue Mountains, the Sawtooth, parts of the
Northern Rockies, the Tetons, and the Wind Rivers. The second
impulse will be displaced a but further north than the lead
shortwave, and WPC probabilities for more than 6 inches are high
in the WA Cascades and Olympics, with moderate probabilities
extending into the Northern Rockies.


Weiss


~~~ Key Messages for the Tennessee Valley through Northeast Winter
Storm ~~~

- Periods of heavy snow will continue across Northern New England
through early Sunday bringing an additional 3-6 inches of
snowfall. This snow will combine with gusty winds to produce
hazardous travel and isolated power outages.

- Elsewhere across the Northeast, brief heavy snow showers and
isolated snow squalls may produce reduced visibility and hazardous
travel.

- Behind the storm, record cold is likely for much of the
Southeast tonight as temperatures fall below freezing as far south
as the Gulf Coast and northern Florida.

- With rapidly falling temperatures tonight, untreated surfaces
that remain wet will re-freeze, leading to slippery roadways and
sidewalks.

$$




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FOUS11 KWBC 130823
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
422 AM EDT Sun Mar 13 2022

Valid 12Z Sun Mar 13 2022 - 12Z Wed Mar 16 2022

...Pacific Northwest...
Days 1-3...

The first of two distinct shortwaves has moved onshore
Washington/Oregon overnight, accompanied by Pacific jet energy and
a surface cold front. This feature will dig southward towards the
Four Corners region today, with shortwave ridging following close
behind into the Pacific Northwest later today. This will allow
heavy snowfall to gradually taper off from west to east. Prior to
the end of heavy snowfall, WPC probabilities are high for 6+
inches in the Oregon Cascades, with moderate probabilities
extending into the Blue Mountains, the Sawtooth, parts of the
Northern Rockies, the Tetons, and the Wind Rivers. Moderate
probabilities also look to extend farther south into the Uinta and
Elk Mountains of Utah and Colorado, respectively, as the shortwave
digs southward. The second shortwave/impulse will be less compact
and displaced a bit farther north than the lead shortwave, and WPC probabilities for more than 6 inches are high in the WA Cascades
and Olympics on D2/D3 in association with the shortwave. This
secondary impulse looks to open up into a large scale trough on
D3, and moderate probabilities then extend into the Northern
Rockies, the Sawtooth, and the Tetons once again.


...Upper Midwest...
Day 2...

A potent jet streak racing west to east across the Northern Plains
and Upper Midwest will drive ascent atop an elevated baroclinic
gradient north of a cold front sinking into the Mid-Mississippi
Valley. A weak wave of low pressure along this front will shift
southeast, driving subtly enhanced warm advection which will
isentropically ascend the Canadian high to produce an expanding
precipitation shield from North Dakota through the western Great
Lakes. The most robust overlap of forcing and moisture is likely
from eastern MN through the U.P. and into the northern L.P. of MI,
where some enhanced fgen is likely to drive heavier snow rates.
This feature will move quickly eastward, but WPC probabilities for
more than 4 inches have increased to as high as 10-30% in a narrow
corridor from WI through the U.P. of MI.


Churchill/Weiss

$$




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FOUS11 KWBC 132051
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
451 PM EDT Sun Mar 13 2022

Valid 00Z Mon Mar 14 2022 - 00Z Thu Mar 17 2022

...Upper Mississippi Valley into the Upper Great Lakes...

Day 1...

A 110-120kt 250mb jet streak traversing northern MN, far northern
WI, and Upper MI and ensuing right-entrance region forcing to the
south will focus deep-layer ascent in a narrow ribbon to the south
across from central to southeast ND into central MN, then eastward
through portions of northern WI, far southern Upper MI, and
northern Lower MI. Given the narrow nature of the most favorable
low-mid level frontogenesis, there continues to be some
latitudinal spread among the guidance in terms of where the best
band(s) will set up, which is largely dependent upon what layer(s)
the models are indicating upward motion. The GFS and corresponding
high-res CAM (FV3) show stronger ascent within the dendritic
growth zone (DGZ), and as a result, is a wet outlier with the QPF

0.50") and SLR, and as a result has heavier max snow totals

(6-7" per GFS, 8-9" per the FV3). The latest WPC forecast, owing
to the NBM and HREF trends, was a little farther south with the
highest 24 hour probabilities of 4+ inches compared to last
night's forecast (>50% from portions of north-central WI into
Charlevoix, southern Emmet, northern Antrim Counties in northwest
Lower MI). 700-500 mb theta-e lapse rates between +1 to +2C would
imply weak symmetric stability, and as such anticipate one main
west to east frontogenetic band, likely leading to an average of
4-6" of snow with locally higher amounts. The latest (12Z) HREF in
fact shows a few members showing >0.05"/hr QPF within this region
between 13-20Z Monday.

The probability of freezing rain exceeding 0.10" is less than 10
percent during days 1 through 3.

Hurley

$$




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FOUS11 KWBC 132131
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
530 PM EDT Sun Mar 13 2022

Valid 00Z Mon Mar 14 2022 - 00Z Thu Mar 17 2022

...Upper Mississippi Valley into the Upper Great Lakes...

Day 1...

A 110-120kt 250mb jet streak traversing northern MN, far northern
WI, and Upper MI and ensuing right-entrance region forcing to the
south will focus deep-layer ascent in a narrow ribbon across
central to southeast ND into central MN, then eastward through
portions of northern WI, far southern Upper MI, and northern Lower
MI. Given the narrow nature of the most favorable low-mid level
frontogenesis, there continues to be some latitudinal spread among
the guidance in terms of where the best band(s) will set up, which
is largely dependent upon what layer(s) the models are indicating
the strongest vertical motion. The GFS and corresponding high-res
CAM (FV3) show stronger ascent within the dendritic growth zone
(DGZ), and as a result, is a wet outlier with the QPF (>0.50") and
SLR, and as a result has heavier max snow totals (6-7" per GFS,
8-9" per the FV3). Most of the other models show max UVVs either
above or below the DGZ. The latest WPC forecast, owing to the NBM
and HREF trends, was a little farther south with the highest 24
hour probabilities of 4+ inches compared to last night's forecast

50% from portions of north-central WI into Charlevoix, southern

Emmet, northern Antrim Counties in northwest Lower MI). 700-500 mb
theta-e lapse rates between +1 to +2C would imply weak symmetric
stability, and as such anticipate one main west-east frontogenetic
band, likely leading to an average of 4-6" of snow with locally
higher amounts. The latest (12Z) HREF in fact shows a few members
showing >0.05"/hr QPF within this region between 13-20Z Monday,
imlying potentially 0.5-1.0"/hr snowfall rates for at least a few
hours during the peak of the event.

The probability of freezing rain exceeding 0.10" is less than 10
percent during days 1 through 3.

Hurley

$$




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FOUS11 KWBC 140839
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
438 AM EDT Mon Mar 14 2022

Valid 12Z Mon Mar 14 2022 - 12Z Thu Mar 17 2022

...Upper Great Lakes...
Day 1...

A 110-120kt 250mb jet streak traversing Ontario and Quebec will
provide deep-layer ascent via the right-entrance region in a
narrow ribbon across central MN eastward through portions of
northern WI into the southern U.P. and northern L.P of MI. Hi-res
guidance has come into better agreement with the latest cycle
regarding the latitudinal placement of the most favorable low-mid
level frontogenesis and resulting heavy snow band, but some spread
still exists given the very narrow nature of this feature. With
regard to intensity, there is also better agreement that the best
lift will occur outside (above and below) the DGZ, which has
resulted in a meaningful decrease in WPC probabilities for greater
than 4 inches of snow (down to a peak of 20-40% odds over portions
of NE WI and the far southern U.P of MI). The more bullish hi-res
members include the ARW, ARW2, NAM-nest, and HRRR which depict
localized totals in excess of 6 inches. The latest WPC forecast
calls for an average of 3-5" of snow along this west-east oriented
band, but locally higher amounts are certainly possible where the
more idealized lift within the DGZ is realized.


...Pacific Northwest into the Rockies...
Days 1-3...

Another distinct shortwave trough will move ashore the Pacific
Northwest later tonight, opening up into a large scale trough
while deamplifying/stalling out on D2 as the synoptic pattern
becomes more blocked. WPC probabilities for more than 6 inches are
high in the WA Cascades and moderate in the Olympics on D1/D2,
with moderate probabilities then extending into the OR Cascades,
portions of the northern Rockies, Sawtooths, and Teton Range on
D2. The trough looks to re-amplify as it crawls slowly east on D3,
due to ridging upstream over the Pacific Northwest. This sends
moderate probabilities for more than 6 inches farther south into
the Rockies and Front Range.


Churchill

$$




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FOUS11 KWBC 142033
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
432 PM EDT Mon Mar 14 2022

Valid 00Z Tue Mar 15 2022 - 00Z Fri Mar 18 2022

...Interior Northeast...
Days 1/2...

The impulse currently driving the snow bands over northern WI/MI
will shift some bands over far northern NY into VT this evening.
Then a stronger impulse shifts east from Lake Huron Tuesday with
some weak surface low development and banding a bit farther south.
12Z consensus has this secondary banding over Lake Ontario
Tuesday, shifting east across north-central New England Tuesday
night. Marginal thermals accompany both waves with accumulating
snow mostly limited to where decent precip rates develop due to
dynamic cooling. Day 1 WPC snow probabilities for over 4" are
limited to the northern Adirondacks and the Presidential Range in
NH for Day 1.5. Probabilities for over 2" do cover most of the far
northern New York west of Lake Champlain, spreading over the
higher terrain of northern VT/NH for Day 1.5.


...Pacific Northwest through the Rockies...
Days 1-3...

The active pattern continues in the Pacific Northwest with the
next wave reaching the shore late tonight and widespread moderate
precip in an atmospheric river crossing the WA/OR coasts later
this afternoon with mountain snows for the Cascades and Northern
Rockies through Tuesday. Snow levels will be elevated, ranging
from about 5000ft in WA to over 7000ft in CA and 5000 to 6000ft
over the northern Rockies. Day 1/1.5 WPC probabilities for over 6"
are than 6 inches remain high for the WA Cascades and moderate
for the OR Cascades, and the northern Rockies of MT and ID. A
reinforcing trough digs over the southern Great Basin Wednesday
setting up lee cyclogenesis over the southern High Plains to
combine with high pressure shifting down the northern Rockies
Wednesday night to bring precip in a marginally cold profile to CO
Wednesday night, shifting into northeast NM Thursday. Day 3 snow
probabilities for over 6" are moderately high over the eastern
slopes of the CO Front Range, Palmer Divide, and down the Sangre
de Cristos into NM.

A weak wave reaching the Pacific Northwest Thursday with mainly
light snow above levels around 4000ft. Day 3 snow probabilities
for over 4" are low over the northern WA Cascades.


The probability for receiving at least 0.1" of freezing rain is
next to zero across the lower 48 Days 1-3.

Jackson

$$




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FOUS11 KWBC 150728
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
327 AM EDT Tue Mar 15 2022

Valid 12Z Tue Mar 15 2022 - 12Z Fri Mar 18 2022

...Interior Northeast...
Days 1...
Minor troughing over the Great Lakes and Northeast with a few
embedded impulses will move through. A stationary boundary draped
through the area combined with the mid/upper level forcing for
ascent will bring a narrow frontogenetical band of light snow to
the interior Northeast toward central Maine through this evening.
Accumulations will generally be light with some slight to moderate probabilities for 2-4" over the NY Adirondacks and Presidential
Range in NH.


...Pacific Northwest through the Rockies...
Days 1-3...
Plume of Pacific moisture streams onshore across the Northwest
today/tonight associated with a longwave trough will bring
widespread precipitation to the region. Snow levels mostly above
5000-7000 ft will confine the greatest snow accumulations to the
peaks of the Olympics and WA Cascades. As the moisture spreads
inland, heavier snow reaches the northern Rockies. WPC
probabilities are high for 6" or more for the WA Cascades and
reach moderate levels for ID and northwest MT.

A reinforcing trough digs over the Great Basin Wednesday resulting
in lee cyclogenesis over the southern High Plains. Meanwhile,
strong high pressure nosing south from the northern Plains will
result in a tight pressure gradient favoring upslope flow over the
Front Range. Temperatures are marginally supportive for wet snow,
greatest in the higher terrain region. The latest WPC
probabilities for 6 inches or more are 50 to 80 percent where some
isolated double digit totals are possible.

A reinforcing trough digs over the southern Great Basin Wednesday
setting up lee cyclogenesis over the southern High Plains to
combine with high pressure shifting down the northern Rockies
Wednesday night to bring precip in a marginally cold profile to CO
Wednesday night, shifting into northeast NM Thursday.

For Days 1-3, the probability for receiving at least 0.1" of
freezing rain is less than 10 percent across the lower 48.

Taylor

$$




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FOUS11 KWBC 151958
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
357 PM EDT Tue Mar 15 2022

Valid 00Z Wed Mar 16 2022 - 00Z Sat Mar 19 2022


...Pacific Northwest through the Rockies...
Days 1-3...
A frontal band associated with a broad upper trough will continue
to move through the northern Rockies, producing mostly light to
moderate accumulations across the region this evening and
overnight. Widespread heavy amounts are not expected, however
there is the potential for locally amounts across the higher
terrain of the northern Idaho, northwestern and southern Montana,
and northwestern Wyoming ranges. WPC probabilities indicate at
least a moderate risk (40 percent or greater) for snow
accumulations of 4 inches or more across parts of those areas.
Meanwhile, continued onshore flow with embedded energy aloft will
support additional snow, with locally heavy accumulations across
the northern Cascades. Snow levels will remain low enough to
support at least a few inches at the pass level, with WPC
probabilities indicating at least a slight risk (10 percent or
greater) for additional accumulations of 4 inches or more at both
Snoqualamie and Stevens passes.

By late tomorrow the upper trough is expected to shift east over
the Rockies. Models show a split in the flow beginning to
develop, with an upper jet couplet centered over the central
Rockies. The associated upper level forcing combined with upslope
flow and low-to-mid level frontogenesis will support snow
developing over the central Rockies beginning Wednesday. The
southern branch of the upper trough is expected to amplify, with
northeasterly flow increasing on the northwest side of a deepening
surface low over the Texas Panhandle. This will support snow
developing east of the Front Range onto the Palmer Divide
Wednesday night into Thursday morning. From the Front Range to
the Sangre de Cristo Mountains and onto the Palmer Divide, WPC
probabilities indicate that accumulations of 4-8 inches are
likely, with a significant threat for locally heavier amounts
especially along the Front Range. The heaviest amounts are
expected to fall west of the I-25 corridor, although portions of
the western Denver Metro may be impacted.

For Days 1-3, the probability for receiving at least 0.1" of
freezing rain is less than 10 percent across the lower 48.

Pereira

$$




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FOUS11 KWBC 151958
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
357 PM EDT Tue Mar 15 2022

Valid 00Z Wed Mar 16 2022 - 00Z Sat Mar 19 2022


...Pacific Northwest through the Rockies...
Days 1-3...
A frontal band associated with a broad upper trough will continue
to move through the northern Rockies, producing mostly light to
moderate accumulations across the region this evening and
overnight. Widespread heavy amounts are not expected, however
there is the potential for locally amounts across the higher
terrain of the northern Idaho, northwestern and southern Montana,
and northwestern Wyoming ranges. WPC probabilities indicate at
least a moderate risk (40 percent or greater) for snow
accumulations of 4 inches or more across parts of those areas.
Meanwhile, continued onshore flow with embedded energy aloft will
support additional snow, with locally heavy accumulations across
the northern Cascades. Snow levels will remain low enough to
support at least a few inches at the pass level, with WPC
probabilities indicating at least a slight risk (10 percent or
greater) for additional accumulations of 4 inches or more at both
Snoqualamie and Stevens passes.

By late tomorrow the upper trough is expected to shift east over
the Rockies. Models show a split in the flow beginning to
develop, with an upper jet couplet centered over the central
Rockies. The associated upper level forcing combined with upslope
flow and low-to-mid level frontogenesis will support snow
developing over the central Rockies beginning Wednesday. The
southern branch of the upper trough is expected to amplify, with
northeasterly flow increasing on the northwest side of a deepening
surface low over the Texas Panhandle. This will support snow
developing east of the Front Range onto the Palmer Divide
Wednesday night into Thursday morning. From the Front Range to
the Sangre de Cristo Mountains and onto the Palmer Divide, WPC
probabilities indicate that accumulations of 4-8 inches are
likely, with a significant threat for locally heavier amounts
especially along the Front Range. The heaviest amounts are
expected to fall west of the I-25 corridor, although portions of
the western Denver Metro may be impacted.

For Days 1-3, the probability for receiving at least 0.1" of
freezing rain is less than 10 percent across the lower 48.

Pereira

$$




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FOUS11 KWBC 211959
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
359 PM EDT Mon Mar 21 2022

Valid 00Z Tue Mar 22 2022 - 00Z Fri Mar 25 2022

...Southern Rockies into the Central Plains...
Days 1-2...

A surface low pressure emerging from the lee of the Southern
Rockies tonight will lift northeast into the MS VLY by Tuesday
evening, and then slowly drift further northeast Wednesday as the
upper trough evolution becomes complex. While this low is not
expected to become exceptionally strong, forcing will be
impressive through robust WAA out of the Gulf of Mexico and strong
jet-level diffluence. The atmospheric column is likely to be too
warm for much snow across most of this area, at least initially,
so the pronounced WAA on 50kts of southerly 850mb wind will lead
to an expansion of rainfall. However, a trailing cold front will
drop southeast immediately behind the wave of low pressure, and
the associated strong CAA will aid in dynamically cooling the
column to cause a changeover from rain to snow. During this
transition, fgen will sharpen in response to the pinched
baroclinic gradient beneath the LFQ of the jet streak, and this
may align with a stretched deformation axis NW of the surface low.
Where these features overlap, a period of heavy snow is likely,
with snowfall rates possibly reaching 2"/hr thanks to CSI and as
forecast by the WPC prototype snowband tool. The guidance has
become more aggressive with snowfall accumulations due to the
rapid changeover, and this is despite low-level temps that will
crash to just around 0C. However, the more rapid changeover
combined with intense ascent should allow snowfall to accumulate
rapidly, and WPC probabilities for 4+ inches have increased on D1
to more than 50%, highest in the TX/OK Panhandle and into western
KS. Locally, more than 6 inches is possible in any of these bands.

As the low pulls further E/NE on D2, forcing is expected to weaken
so only light accumulations reaching around 2 inches is forecast
from eastern NE into the Buffalo Ridge of SD/MN, and residual
light snow is also likely into D2 across the higher terrain of NM
within the broad upper trough axis, where storm-total snowfall
will likely exceed 6 inches in some places.


...Northern Plains through the Great Lakes into the Northeast...
Days 1-3...

A northern stream shortwave trough will cross ND tonight and then
shifts towards the Great Lakes into D2, while eventually merging
with southern stream energy coming out of the Plains to drive a
complex but large scale closed low across the Plains. The
amplified mid-level pattern will allow deep southerly flow to
advect anomalous moisture northward ahead of the northern stream
low, and then more impressively in advance of the phased upper
gyre and associated surface wave ejecting out of the MS VLY. While
moisture will be plentiful, the column will be marginally cold
enough for snow, and a period of freezing rain is likely from
eastern MN through the western Great Lakes in response to the slow
retreat of Canadian high pressure.

On D1, WPC probabilities for 4 inches of snowfall are 10-30%
across northern MN, with a local maxima above 50% in the Arrowhead
where moist advection off Lake Superior will efficiently upslope
into the Iron Ranges to increase snowfall. While some freezing
rain is also likely in the Arrowhead D1, this is likely to
transition to snow the latter part of D1, and more impressively on
D2 in response to deeper moisture out of the Gulf lifting
northward. WPC probabilities on D2 for 4+ inches are above 80% in
the Arrowhead, and storm total snowfall could exceed 12 inches in
some places. Heavy snow will also extend eastward into the Great
Lakes on D2, with WPC probabilities for more than 4 inches
reaching as high as 50% in the eastern U.P. of MI.

As the warm nose overruns the cold surface air, a period of
freezing rain is likely in eastern MN and the U.P. of MI D1 where
WPC probabilities for 0.1" of accretion reach above 50%, highest
in the arrowhead, and then shift eastward with decreasing
probabilities in the northern L.P. of MI on D2. Finally, as the
best WAA shifts into the Northeast on D3, WPC probabilities
indicate a better than 40% chance for 0.1" of freezing rain in the
Adirondacks, Catskills, Berkshires, and Green Mountains.


Weiss

$$




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FOUS11 KWBC 220849
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
449 AM EDT Tue Mar 22 2022

Valid 12Z Tue Mar 22 2022 - 12Z Fri Mar 25 2022

...Central and Northern Great Plains through Minnesota...
Days 1-2...

An occluded low pressure system drifts northeast from OK early
this morning, across MO through tonight, and to lower MI through
Wednesday night. Reinforcing waves/impulses will make the system
rather complex and sprawling. Exceptional moisture streaming ahead
of this system out the Gulf of Mexico and strong jet-level
diffluence makes for low-level frontal bands of snow to continue
to lift northeast up the Plains today, continuing over the
Arrowhead of MN into tonight. These dynamic bands will continue to
allow embedded snow to develop in the banding from west-central KS
into east-central Neb and slowly shift northeast across MN today.
Notable enhancement will come from the left exit region of the
southerly jet streak currently developing over eastern OK that
darts north through IA this morning and western WI this afternoon.
The 00Z HREF limits snowfall rates over 1"/hr to eastern Neb
through mid-morning, but the persistence of the snow over MN
could also allow decent snowfall in that stripe. Day 1 snow
probabilities for over 2" are low to moderate in a stripe over
eastern Neb through southwestern MN (highest on Buffalo Ridge
where over 4" is most likely).

Areas farther north over northern MN will have lake enhancement as
well that the same left exit region upper level lift. There should
be several areas of far northeastern MN that have snow over 6"
including the North Shore escarpment.


...Great Lakes through the Northeast...
Days 1-3...

The sprawling low lifting northeast from eastern OK through MO
today will bring deep southerly flow and anomalously high moisture
northward across the Great Lakes today with the warm nose making
for mostly a rain/freezing rain decision today (left up to the sfc
temp). However, height falls from the approaching upper low will
allow snow to develop around the U.P. of MI tonight and continue
through Tuesday. Moderate Day 1.5 snow probabilities for over 4"
are over far northern WI and through the central/western U.P. of
MI. A wintry mix will persist in this time with quite the complex
mix of snow/sleet/freezing rain/rain across the northern Great
Lakes. As of now Days 1 and 1.5 ice probabilities are moderate for
0.1" ice from the North Shore of Lake Superior across northern MI
with probabilities for over 0.25" generally limited to 30% for the
Keweenaw Peninsula and the Huron Mtns.

The sprawling low expands into the Northeast Wednesday, continuing
through Thursday night. Warm air advection on this side of the
system does allow some freezing rain to occur mainly in elevation
across the Northeast. Days 2 WPC ice probabilities for over 0.1"
are moderate Adirondacks, Catskills, Berkshires, and Green
Mountains, expanding to include the White Mtns of NH/Maine for Day
3.


Jackson

$$




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FOUS11 KWBC 221953
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
353 PM EDT Tue Mar 22 2022

Valid 00Z Wed Mar 23 2022 - 00Z Sat Mar 26 2022

...Great Lakes through the Northeast...
Days 1-3...

As a sprawling low lifts through the Plains this evening,
southerly flow will drive anomalously high moisture northward
through the Great Lakes. The combination of the warm nose reaching
the region as well as the closed low wobbling overheard will make
for a messy, long duration ptype scenario for potential of
freezing rain/rain but also accumulating snow and sleet. Marginal
surface temps and colder heights aloft as the closed low moves
overhead, with embedded pieces of vorticity, will create a mix of
ptypes. The greatest snowfall accumulations look to be favored for
the North Shore given strong easterly flow upsloping against the
terrain. Here, moderate to high probabilities of 6" or more exist
while across the U.P., 4" probabilities are slight to moderate.
While more uncertainties exist in the evolution and potential of
ice accumulation, there is a signal for some ice accumulations of
0.1", particularly for northern WI and L.P. of MI.

As the occluded low reaches the Great Lakes, its warm advection
wing of precipitation is expected to reach the Northeast late
Wednesday night into Thursday morning. Depending on the surface
temperatures, some freezing rain may develop particularly across
the elevation areas of the Catskills and Adirondacks of NY, Greens
of VT, MA Berkshires, and the Whites of NH/Maine. WPC ice
probabilities of at least 0.01" are high with moderate
probabilities of more substantial accumulations of 0.1".

Taylor

$$




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FOUS11 KWBC 230835
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
433 AM EDT Wed Mar 23 2022

Valid 12Z Wed Mar 23 2022 - 12Z Sat Mar 26 2022

...Upper Great Lakes...
Days 1-3...

A sprawling low drifts northeast from northern IL over lower MI
through tonight. Height falls ahead of the approaching upper low
counter acts the low level warm air advection to allow a
changeover from rain/freezing rain to snow this morning across
northern WI/the U.P. of MI where some banding with snowfall rates
up to 1"/hr can be expected. Day 1 snow probabilities are low to
moderate for 4" over far northern WI and the higher elevations of
the U.P. with most snow ending by evening as precip rates decrease
north of the occluded low. Some additional light freezing rain is
likely in pockets this evening with low probabilities for a tenth
inch over northern MI.

A clipper shifts southeast from ND to the Midwest Friday. Lake
enhancement off Superior allows for some low to moderate Day 3
snow probabilities for over 4" over the western U.P. of MI.


...Northeast...
Days 1-3...

Warm advection precipitation ahead of the sprawling low over the
Midwest will cross the Northeast this evening through Thursday
morning. Sufficiently cold air is retained on the terrain to allow
freezing rain of the Catskills and Adirondacks of NY, Greens of
VT, MA Berkshires, and the Whites of NH/Maine where Days 1 and 2
WPC ice probabilities for over 0.1" are moderately high.

A reinforcing trough rounding the upper low will allow coastal low
development over the northern Mid-Atlantic late Thursday with
rapid development as the low quickly lifts past Maine early
Friday. A transition from plain rain near the coast to freezing
rain and sleet over interior Maine and snow up in Aroostook occurs
Thursday night. Day 2 snow probabilities over 4" are moderately
high over far northern Maine with low probabilities for over 0.1"
ice extending through north-central Maine.


Jackson

$$




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FOUS11 KWBC 232029
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
428 PM EDT Wed Mar 23 2022

Valid 00Z Thu Mar 24 2022 - 00Z Sun Mar 27 2022

...Upper Midwest/Great Lakes...
Days 1-3...
A wintry mix associated with a broad area of low pressure lifting
northeast across the Midwest/Great Lakes is expected to produce
some additional snow and ice accumulations through this evening
across portions of the northern Great Lakes region. For most
areas, accumulations are expected to be light. For the evening
into the overnight period, guidance does show an area of strong
upper divergence associated with left-exit region upper jet
forcing centered over northern Lower Michigan and the eastern U.P.
This may raise the potential for heavier precipitation rates and
is reflected in localized higher WPC probabilities for additional
ice accumulations of 0.10 inch or more and 1-2 inches of snow
across the region during the evening to overnight hours.

On Friday, a well-defined clipper system is forecast to dive
southeast across the Upper Midwest. This is expected to bring
some synoptic, mainly light snows from eastern North Dakota across
northern Minnesota on Friday. Lake effect snows downstream of the
upper lakes are expected to develop by late Friday and continue
into the weekend. A prolonged period of northwesterly flow could
support some locally heavy amounts in the U.P. and northern Lower
Michigan.

...Northeast...
Days 1-2...
Warm advection precipitation associated with the low over the
Midwest will continue to spread north across the Northeast this
evening, through the overnight, and into tomorrow. As warm air
aloft spreads across the region, models continue to show a shallow
cold air wedge developing at the surface. This will support a
wintry mix, with accumulating ice likely across the higher
elevations of northeastern Pennsylvania, eastern Upstate New York,
into central and northern New England tonight into tomorrow. For
the Catskills, Adirondacks, Berkshires, and Greens -- WPC
probabilities indicate that ice accumulations of 0.10 inch or more
are likely across portions of those areas.

As a well-defined shortwave moving through the base of the broader
scale trough lifts into the Northeast, a low is expected to
develop and track along the Northeast coast Thursday night into
Friday morning -- bringing the potential for significant wintry
precipitation across northern Maine. In the WPC guidance, high
probabilities for snow accumulations of 4 inches or more are
indicated across northern Aroostook County.

...Central Appalachians...
Day 3...
The clipper system sliding across the Upper Midwest on Friday is
expected to continue across the Ohio Valley and central
Appalachians on Saturday. This is forecast to be a very dynamic
system, with models indicating a closed 500 mb center dropping
southeast from the Great Lakes into the Ohio Valley Friday night.
Strong forcing aloft along with upslope flow may support a period
of at least moderate snow across the higher elevations of the
southern Allegheny mountains early Saturday. In the wake of the
system, deep northwesterly flow and strong cold air advection will
likely support lake effect and orographic snows from the Lower
Great Lakes into the central and southern Appalachians. Heaviest
snow accumulations are excepted to focus along the southern
Allegheny Mountains, where WPC probabilities indicate that 2-4
inches are likely, with heavier amounts possible across the higher
terrain.

Pereira

$$




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FOUS11 KWBC 240839
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
438 AM EDT Thu Mar 24 2022

Valid 12Z Thu Mar 24 2022 - 12Z Sun Mar 27 2022

...Upper Midwest/Great Lakes/Central Appalachians
Days 2-3...

A shortwave digging out of Alberta, Canada will strengthen into a
closed low Saturday morning as it dives across MN and into the
Great Lakes. This feature will continue to dig southeast across
the Mid-Atlantic Saturday night into Sunday before weakening and
ejecting into Canada. This will drive an elongating trough across
the eastern CONUS, with a trailing jet streak strengthening to
130kts across the Upper Midwest Saturday night. A surface wave
beneath the mid-level impulse will move along the international
border and then into the Great Lakes, driving a cold front
southeastward to off the east coast Saturday, followed by a
reinforcing shot of cold air quickly in its wake. While forcing is
transient and moisture is somewhat limited, periods of heavy snow
are likely across the region.

On D2, some moderate snowfall is expected in the vicinity of the
primary shortwave across the MN Arrowhead. The guidance,
especially the high-res members, shows some loss of saturation
within the DGZ, but the global members are a little wetter, and
there is sufficient forcing to squeeze out any moisture as
snowfall. WPC probabilities for 4+ inches have fallen, bu are
still 10-20%. A secondary maxima of snowfall D2 is likely south of
Lake Superior and into the Bayfields Peninsula where CAA will
steepen the low-level lapse rates and produce moderate LES.

On D3, the trough axis swings eastward, and the associated CAA
will spread LES downwind of Lake Erie and Lake Ontario. Snowfall
may be heavy at times, especially along the Chautauqua Ridge and
westerns lopes of the Adirondacks where WPC probabilities for more
than 4 inches are 20-30%. A secondary maxima of snow, and likely
the the most impressive, is forecast along the upwind side of the
Central Appalachians near WV, western MD, and southwest PA, where
pronounced upslope flow will drive periods of heavy snowfall, at
least through Saturday evening before the DGZ begins to dry out.
In the higher terrain, WPC probabilities for more than 4 inches on
D3 are above 80%, and locally 10 inches of snowfall is possible.


...Northeast...
Days 1-2...

A wave of low pressure across the Mid-Atlantic this morning will
slowly deepen as it shifts northeast into New England tonight and
then into Canada on Saturday. This low will deepen only slowly as
a broad but deep mid-level trough shifts eastward, and downstream
jet energy pivots eastward placing LFQ diffluence across the
Northeast. A modest warm front extending eastward from the surface
low will weaken, but persistent WAA on southerly low-level flow
will help to expand precipitation into New England through
Saturday, with a mix of snow and ice likely as the cold surface
high gradually retreats. The threat for heavy snow is likely
confined to far northern Maine, generally just Aroostook County,
as the low tracks along the coast. Guidance has gotten a little
colder tonight, but WPC probabilities for more than 4 inches of
snow remain above 50% just in far northern ME on D1 and D2.

Further to the south, the mix of sleet and freezing rain will
likely lead to rounds of accumulating ice, primarily in the
elevated regions of central and northern New England. WPC
probabilities for more than 0.1" of freezing rain are as high as
40% in the White Mountains of NH and Central Highlands of ME, with
lower probabilities extending into the southern Greens of VT and
Monadnocks of NH.


Weiss

$$




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FOUS11 KWBC 241930
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
329 PM EDT Thu Mar 24 2022

Valid 00Z Fri Mar 25 2022 - 00Z Mon Mar 28 2022

...Upper Midwest/Great Lakes/Central Appalachians...
Days 2-3...

A shortwave trough in south-central Canada will strengthen into a
potent closed low over Lake Erie Saturday morning. Latest 12Z GFS
shows 500mb heights are as low as 2.5 standard deviations below
normal over Ohio. 850mb temperatures as cold as 2 standard
deviations below normal rushing over Lake Superior will trigger
lake effect snow showers with heavy snowfall rates likely within
these bands. Closer to the Ohio Valley and the central
Appalachians, abnormally cold temperatures aloft combined with
peak heating in late March will foster steep low level lapse
rates. A ~110 knot 500mb jet streak over central Illinois
positioning its left exit quadrant atop the upper Ohio Valley and
central Appalachians will promote vertical ascent within the
atmospheric column as well, giving rise to the potential for snow
squalls tracking through these regions. Add in a brisk upslope
flow component into the central Appalachians and snowfall rates
will be heavy at times early Saturday morning and throughout much
of Saturday.

Latest 12Z HREF probabilities indicate a 20-40% chance for
snowfall rates exceeding 1" per hour between 06-12Z Saturday. 3km
NAM model soundings between 12-18Z Saturday in eastern WV also
showed up to ~250 J/kg MUCAPE available, suggesting similar
snowfall rates may continue into the daytime hours. Snowfall rates
should diminish Saturday night and into Sunday in the central
Appalachians as the best forcing moves east, but continuous
upsloping NW flow will keep periods of snow in the forecast into
Sunday morning. Latest WPC probabilities of >4" of snowfall on
Saturday range between 50-90% in eastern WV with a 20-30% chance
for totals exceeding 8". Farther north, lake effect snow off Lake
Erie could lead to locally heavy snow in northwest PA and western
NY on Saturday. WPC probabilities show a 20-30% chance for snow
totals exceeding 4" Saturday with similar probabilities just
downwind of Lake Ontario near the Tug Hill Plateau on Sunday.

...Northeast...
Days 1-2...

An upper level low tracking northeast through the Ohio Valley this
afternoon will track into the eastern Great Lakes tonight while a
surface low strengthens off the coast of Maine. This is in
response to upper level diffluence beneath the right entrance
quadrant of a jet streak over eastern Quebec tonight. High
pressure in the Canadian Maritime is providing a CAD signature at
low levels over northern New England, which combined with mild
southerly flow aloft will result in an icy overrunning
precipitation event. Latest WPC freezing rain probabilities show a
corridor of 40-50% of freezing rain accumulations greater than a
tenth of an inch. Farther north, colder air and a strengthening
700mb front will prompt a band of heavy snow across northern
Maine. The HREF Snowband Probability Tracker (SPT) does contain
some model members that contain over 1"/hr snowfall rates between
08-18Z Friday. The uncertainty in snow totals lies in the
uncertainty of boundary layer conditions and a quickly encroaching
dry slot in the 700-400mb layer Friday morning. In general though,
the closer to the northern Maine/Canada border, the better the
chances for receiving heavy snowfall accumulations. Latest WPC
probabilities do show a narrow area of 50-70% chance for snowfall
exceeding 4" in far northern Maine. Snowfall is expected to
conclude Friday afternoon as the primary wave of low pressure
tracks north of Nova Scotia.


Mullinax

$$




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FOUS11 KWBC 241954
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
353 PM EDT Thu Mar 24 2022

Valid 00Z Fri Mar 25 2022 - 00Z Mon Mar 28 2022

...Upper Midwest/Great Lakes/Central Appalachians...
Days 2-3...

A shortwave trough in south-central Canada will strengthen into a
potent closed low over Lake Erie Saturday morning. Latest 12Z GFS
shows 500mb heights are as low as 2.5 standard deviations below
normal over Ohio. 850mb temperatures as cold as 2 standard
deviations below normal rushing over Lake Superior will trigger
lake effect snow showers with heavy snowfall rates likely within
these bands. Closer to the Ohio Valley and the central
Appalachians, abnormally cold temperatures aloft combined with
peak heating in late March will foster steep low level lapse
rates. A ~110 knot 500mb jet streak over central Illinois
positioning its left exit quadrant atop the upper Ohio Valley and
central Appalachians will promote vertical ascent within the
atmospheric column as well, giving rise to the potential for snow
squalls tracking through these regions. Add in a brisk upslope
flow component into the central Appalachians and snowfall rates
will be heavy at times early Saturday morning and throughout much
of Saturday.

Latest 12Z HREF probabilities indicate a 20-40% chance for
snowfall rates exceeding 1" per hour between 06-12Z Saturday. 3km
NAM model soundings between 12-18Z Saturday in eastern WV also
showed up to ~250 J/kg MUCAPE available, suggesting similar
snowfall rates may continue into the daytime hours. Snowfall rates
should diminish Saturday night and into Sunday in the central
Appalachians as the best forcing moves east, but continuous
upsloping NW flow will keep periods of snow in the forecast into
Sunday morning. Latest WPC probabilities of >4" of snowfall on
Saturday range between 50-90% in eastern WV with a 20-30% chance
for totals exceeding 8". Farther north, lake effect snow off Lake
Erie could lead to locally heavy snow in northwest PA and western
NY on Saturday. WPC probabilities show a 20-30% chance for snow
totals exceeding 4" Saturday with similar probabilities just
downwind of Lake Ontario near the Tug Hill Plateau on Sunday.

...Northeast...
Days 1-2...

An upper level low tracking northeast through the Ohio Valley this
afternoon will track into the eastern Great Lakes tonight while a
surface low strengthens off the coast of Maine. This is in
response to upper level diffluence beneath the right entrance
quadrant of a jet streak over eastern Quebec tonight. High
pressure in the Canadian Maritime is providing a CAD signature at
low levels over northern New England, which combined with mild
southerly flow aloft will result in an icy overrunning
precipitation event. Latest WPC freezing rain probabilities show a
corridor of 40-50% of freezing rain accumulations greater than a
tenth of an inch. Farther north, colder air and a strengthening
700mb front will prompt a band of heavy snow across northern
Maine. The HREF Snowband Probability Tracker (SPT) does contain
some model members that contain over 1"/hr snowfall rates between
08-18Z Friday. The uncertainty in snow totals lies in the
uncertainty of boundary layer conditions and a quickly encroaching
dry slot in the 700-400mb layer Friday morning. In general though,
the closer to the northern Maine/Canada border, the better the
chances for receiving heavy snowfall accumulations. Latest WPC
probabilities do show a narrow area of 50-70% chance for snowfall
exceeding 4" in far northern Maine. Snowfall is expected to
conclude Friday afternoon as the primary wave of low pressure
tracks north of Nova Scotia.


Mullinax

$$




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FOUS11 KWBC 250757
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
356 AM EDT Fri Mar 25 2022

Valid 12Z Fri Mar 25 2022 - 12Z Mon Mar 28 2022

...Upper Midwest/Great Lakes/Central Appalachians...
Days 1-3...

A complex interaction of mid-level features with a surface wave
and cold front will produce heavy Lake Effect Snow (LES), upslope
snow, and convective snow showers across the region through Sunday.

A shortwave lifting out of the Ohio Valley this morning will be
quickly replaced by a more potent impulse digging out of Alberta
to close off near Chicago this evening. This closed feature is
then likely to continue to dive rapidly southeast into the
Mid-Atlantic Saturday before filling and lifting off to the
northeast Sunday morning. This feature will combine with modest
LFQ diffluence within an upstream jet streak diving out of the
Pacific Northwest to produce large scale ascent across the region.
With only marginal moisture in place (PWs of -1 standard deviation
below the climo mean), this overlap of ascent will generally
result in a swath of light to moderate snow from eastern MN
through the Great Lakes and Ohio Valley, and into the Mid-Atlantic
and Northeast. However, there are likely to be three areas of
enhanced snowfall embedded within this larger swath of
precipitation.

The most impressive snowfall is likely in the favored W/NW snow
belts off the Great Lakes as CAA becomes impressive behind a wave
of low pressure and the accompanying surface cold front. Strong
CAA in the wake of this front will steepen the low-level lapse
rates to super-adiabatic levels, and with lake temperatures
beginning to warm, inversion depths are progged to climb above
5,000 ft. These inversions are not exceptionally impressive, but
the instability off the lakes should enhance local ascent, which
despite modest SLRs should lead to an extended period of LES. For
D1, heavy snow is likely in the western U.P. and Bayfields
Peninsula where WPC probabilities for more than 4 inches of snow
are as high as 50%. The heavy LES shifts eastward D2 to focus
downstream of Lake Erie, especially into the Chautauqua Ridge
where moist flow will efficiently upslope to increase snowfall.
WPC probabilities on D2 for more than 4 inches are above 50% in
this region. Heavy snow may persist on D3 downstream of Lake Erie,
while increasing downwind of Lake Ontario, especially into the Tug
Hill plateau. 2-day snowfall east of Lake Erie and Ontario may
exceed 10 inches in a few places.

Additional heavy snow is likely D2 into D3 along the spine of the
Central Appalachians of WV and into the SW portion of the Laurel
Highlands. In this area, W/NW winds behind the front will drive
moist ascent Saturday, leading to periods of heavy snowfall before
the DGZ begins to dry out late Saturday into Sunday. This snowfall
could be enhanced by increasing instability as the primary
shortwave and PV anomaly swing overhead on Saturday. WPC
probabilities for more than 4 inches are above 80% D2, and total
snowfall Sat-Sun could reach 12 inches in isolated locations of
the higher terrain of WV.

Finally, the potent PV anomaly swinging from MN through the
Mid-Atlantic will be accompanied by increasing instability within
the elevated cold pool noted by 500mb heights approaching -3
standard deviations from the climo mean according to NAEFS
ensemble tables. As this upper low pivots overhead, it will be
accompanied by increasing low-level fgen and surface instability
which could reach 250 J/kg. Forecast soundings indicate a deeply
saturated column with lapse rates greater than moist adiabatic
(indicative of a MAUL), and the high-res guidance is in good
agreement that convective snow showers will develop this aftn
through Saturday evening. While the coverage of these snow showers
may be scattered, the snow-squall parameter is forecast as high as
4, which suggests that isolated snow squalls could be embedded
within this convective snowfall. Despite snow accumulations that
are likely to be minimal as this activity drops southeast from the
Upper Midwest this evening through the Ohio Valley and into the
Central Appalachians/Mid-Atlantic late Saturday, brief snowfall
rates of more than 1"/hr combined with gusty winds could produce
hazardous travel due to limited visibility.


...Northeast...
Day 1...

Sharp 5H shortwave will eject northeast from the Ohio Valley and
over Upstate New York today before shifting into the Canadian
Maritimes by Saturday morning. While this primary shortwave stays
well inland, modest height falls and an increasing upper
ventilation within the RRQ of a poleward streaking jet will drive
slow intensification of a surface low moving over Downeast Maine
today. WAA ahead of this low will expand precipitation into Maine
while a wedge of Canadian high pressure gradually retreats to the
east. This will continue an overrunning scenario with periods of
sleet/freezing rain likely across parts of northern and central
Maine. North of the mixed precipitation, a burst of heavy snow is
likely, generally confined to Aroostook County, as the WAA
impressively upglides to produce a burst of snowfall that could
reach 1"/hr this morning according to the SPC snow band prototype
tool. This heavy snow should be of relative short duration
however, and WPC probabilities for more than 4 inches of snow are
about 20-40%.


Weiss

$$




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FOUS11 KWBC 252017
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
416 PM EDT Fri Mar 25 2022

Valid 00Z Sat Mar 26 2022 - 00Z Tue Mar 29 2022

...Upper Midwest/Great Lakes/Central Appalachians...
Days 1-3...

Strong cyclonic flow over the region with embedded potent
shortwave energy will lead to a busy and wintry regime through
this weekend featuring heavy Lake Effect Snow (LES), upslope snow,
and potentially convective snow showers that could lead to
localized hazardous conditions.

Water vapor imagery this afternoon shows a potent shortwave trough
dropping quickly southeast out of the Upper Mississippi River
Valley and will reach the Chicago area by this evening. This
feature is expected to close off at 500 mb as it swings through
the lower Great Lakes tonight into early Saturday. The forcing for
ascent combined with available moisture will produce light snow
across the Great Lakes and central Appalachians. The more
impressive snowfall totals are favored in the W/NW snow belts off
Lake Superior, Michigan, and Erie where the cold air advection
becomes quite impressive behind the surface front. Steepening low
level lapse rates and supportive lake temperatures should lead to
enhanced local ascent and an extended period of lake effect snow.
The western lakes will see the greatest totals during D1 /ending
00Z Sunday/ while the setup will continue to favor Lake Erie LES
through early D2. WPC probabilities for 4 inches or more are
moderate to high in the favored W/NW snow belt areas off the lakes
with a slight signal for 8" totals off Lake where a prolonged
period of LES is expected.

The anomalously deep/cold heights aloft swinging overhead and W/NW
flow regime will also drive impressive upslope snow over the
favored high terrain of the central Appalachians of WV into the SW
portion of the Laurel Highlands. WPC probabilities for 4 inches or
more are above 60-80 percent and total snowfall through early next
week could total 8-10" with isolated amounts exceeding a foot.

Finally, isolated to scattered convective snow showers are likely
through Saturday evening as the main PV anomaly swings through.
Nearly saturated column with steep lapse rates and some marginal
but sufficient instability favors convective snow showers through
this evening over the Great Lakes and then moving toward the
eastern Great Lakes and Northeast tomorrow and tomorrow evening.
Some isolated stronger convective showers or snow squalls will be
possible with snow rates approaching 1"/hr briefly which could
lead to hazardous travel due to limited visibility.


...Sierra Nevada...
Day 3...

Anomalously deep upper low will approach California during the D3
period and a plume of above normal moisture will stream onshore
and directed at the Sierra Nevada. Favorable forcing for ascent /
upper diffluence interacting with the moisture will combine to
produce widespread precipitation late Sunday into Monday. This
system is relatively warm so snow levels will be high, but the
higher peaks of the Sierra are expected to see heavy snow where
the latest WPC probabilities for 4 inches or more are high for the
highest peaks with a slight to moderate signal already for 8" or
greater totals during D3.


Weiss/Taylor

$$




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FOUS11 KWBC 260728
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
327 AM EDT Sat Mar 26 2022

Valid 12Z Sat Mar 26 2022 - 12Z Tue Mar 29 2022

...Upper Midwest/Great Lakes/Central Appalachians...
Days 1-3...

Longwave trough centered over the Great Lakes will maintain broad
cyclonic flow across the East into early next week. Within this
longwave trough, a potent closed mid-level low will dig from
Minnesota to Ohio tonight, and then shift into the Canadian
Maritimes while filling on Sunday. Impressive height falls and PVA
will drive robust synoptic ascent, while a surface low moving
along the international border drags a cold front eastward. While
the synoptic lift is impressive, available moisture is modest
noted by PW anomalies of -0.5 to -1 standard deviations from the
climo mean. This suggests that despite a broad swath of light
snow, the heaviest snow will be confined to the LES snow bands and
into upslope regions where moisture is enhanced, or can be more
efficiently squeezed out into snow.

On D1, the heaviest snowfall is likely SE of Lake Erie along the
Chautauqua Ridge where LES will also upslope to produce heavy snow
rates, especially beginning this evening and persisting through
Sunday aftn. WPC probabilities for more than 4 inches here are
above 70%, and locally more than 8 inches is possible.
Additionally heavy LES is likely into the Tug Hill Plateau,
eastern U.P. southeast of Lake Michigan, and near Traverse City,
MI, where WPC probabilities for more than 4 inches is 10-30%. Also
on D1, enhanced moisture from the lakes will be wrung out
efficiently by prolonged upslope flow into the Central
Appalachians of WV into the Laurel Highlands of PA where more than
6 inches of snow is likely in the higher terrain. By D2, the
continued cyclonic flow and CAA will drive more LES east of Lake
Erie into the Chautauqua Ridge and east of Lake Ontario along the
Tug Hill Plateau and into the western Adirondacks. Additionally
snow accumulations may reach 4 inches on D2, and storm total may
exceed 12 inches near Erie, PA.


Additionally, guidance continues to suggest scattered convective
snow showers developing through Saturday evening as the main PV
anomaly swings eastward from the Ohio Valley into the
Mid-Atlantic. A nearly saturated column with steep lapse rates and
some marginal but sufficient instability favors convective snow
showers beneath the cold pool aloft, with briefly heavy snowfall
rates likely. Although likely to be isolated, the combination of
gusty winds and heavy snowfall may produce embedded snow squalls
as well.


...Sierra Nevada...
Days 2-3...

An anomalously deep upper low characterized by 700mb heights of
more than 3 standard deviations below the climo mean will shift
onshore central CA Monday accompanied by a surface low which will
approach the coast D3 as well. Downstream of this feature, warm
and moist advection will surge onshore as a weak AR (IVT < 500
kg/m/s) within confluent mid-level flow and the LFQ of a 130kt
upper jet streak. Where this flow upslopes into the terrain, heavy
snowfall will become likely late D2 and especially D3 as the core
of the AR shifts across the Sierra. Moderate snowfall is likely
D2, but on D3 WPC probabilities for more than 6 inches of snow
eclipse 70% above 6000 ft, with locally more than 12 inches
possible in the highest terrain, and this will likely produce
hazardous travel across most of the Sierra Passes.


Weiss

$$




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FOUS11 KWBC 262019
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
417 PM EDT Sat Mar 26 2022

Valid 00Z Sun Mar 27 2022 - 00Z Wed Mar 30 2022

...Great Lakes/Central Appalachians...
Days 1-2...
An amplified longwave trough will remain positioned over the
eastern U.S. through Monday before a ridge begins to shift east
across the Great Lakes on Tuesday. The continuance of deep
cyclonic flow with embedded energy aloft will contribute to
additional lake effect/enhanced showers before diminishing in the
lee of the northern Great Lakes early Monday and then tapering off
later in the day downwind of the eastern Great Lakes. With
contributing moisture from Lake Huron and wraparound moisture from
a consolidating low over the Gulf of St. Lawrence/Atlantic Canada,
the heaviest amounts from this evening into Monday are expected to
line up along the higher elevations southeast of Lake Erie. For
the 48 hour period ending 00Z Tuesday, WPC probabilities indicate
that accumulations of 8 inches or more are greater than 50 percent
in the upslope areas of northwestern Pennsylvania and western New
York. Locally heavy amounts are also possible in the Tug Hill
region, although veering winds are expected to result in less
favorable conditions.

Additional snows are likely in the upslope regions of the central
Appalachians as well, with at least a couple more inches of
accumulation likely this evening/overnight along the Allegheny
Mountains.

...California to the Rockies...
Days 2-3...
An anomalously deep upper low developing over the eastern Pacific,
west of California, is forecast to impact the region by early
Monday. Deep southwesterly flow ahead of the approaching low,
along with left-exit region upper jet dynamics, will contribute to
the development of heavy snow along the higher elevations of the
central and southern Sierra Nevada. Snow is expected to continue
into Monday night as the low moves across the region. Widespread
snow accumulations of 4-8 inches are likely, with locally heavier
amounts expected, especially for areas above 7000 ft. Locally
heavy accumulations are also possible across the higher peaks of
the Southern California Transverse Ranges.

As the low continues east, high elevation snows are forecast to
develop over portions of the Great Basin, Arizona, and the central
Rockies. Heavy accumulations are most likely across the San Juan
Mountains in southwestern Colorado, where deep southwesterly flow,
along with favorable upper forcing are expected to once again
contribute to heavier rates.

Meanwhile to the north, widespread but generally light
accumulations associated with a northern stream trough can be
expected late Monday into Tuesday across the northern Rockies into
the northern Plains.

Pereira

$$




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FOUS11 KWBC 270815
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Sun Mar 27 2022

Valid 12Z Sun Mar 27 2022 - 12Z Wed Mar 30 2022

...Great Lakes...
Day 1...

Continued cyclonic flow around a longwave trough axis slowly
shifting into the western Atlantic will maintain CAA and lake
effect snow in the favored W/NW snow belts today. Although
moisture and forcing should diminish through the day, persistent
inversion heights around 6000 ft and good forcing into the
lowering DGZ will allow LES to persist much of D1 with a slow wane
in coverage and intensity this evening. In the areas that see the
most LES, generally the Chautauqua Ridge and the Tug Hill Plateau,
WPC probabilities for an additional 4+ inches after 12Z this
morning are 30-50%. Tonight moisture should wane more rapidly, but
lingering streamers, especially where the effective fetch includes
Lake Huron or Georgian Bay, could produce additional light
accumulations through early Monday.


...California to the Rockies...
Days 1-3...

An anomalously deep 500mb low will swing onshore the central CA
coast Monday aftn and then slowly fill into an open wave across
the Southwest Tuesday evening. Confluent and fast flow downstream
of this trough will combine with a strengthening subtropical jet
streak of 130kts arcing into southern CA to spread deep column
moistured noted by PWs of +2 standard deviations into the Great
Basin. This will manifest as periods of heavy precipitation, which
above 6000 ft will be snow.

On D2, heavy snow is expected in the Sierra where impressive
moisture, deep layer ascent, and enhanced omega as mid-level flow
upslopes favorably into the terrain will overlap. WPC
probabilities for more than 6 inches are above 90%, and locally
12-15" of snow is possible. Significant pass level snow is likely
D2 as well, including Donner Pass. While the best overlap of
ascent and moisture is likely to be in the Sierra, as the entire
trough shifts eastward in tandem with the upper jet streak, heavy
snow will spread into the Great Basin and Central Rockies on D3.
WPC probabilities for more than 6 inches of snow reach as high as
50% Tuesday in the White Mountains of AZ, the San Juans, the
Uintas, the Wind Rivers, and much of the CO Rockies.


...Upper Midwest through the Mid-Atlantic...
Day 3...

A potent southern stream shortwave will eject out of the Southwest
on Tuesday and likely deepen into a closed low across the Central
Plains by the end of the forecast period. At the same time,
northern stream energy digging out of Alberta will drop rapidly
into the Dakotas, and these features will try to phase late D3 and
beyond. While the guidance has backed off slightly on the
interaction of these features, at least some phasing combined with
intensifying diffluence within the LFQ of a subtropical jet streak
will cause a deepening surface low to move out of the Rockies and
towards the Great Lakes D3. The guidance continues to feature a
wide variation in low placement and speed, leading to lowered
confidence in the evolution as the system moves northeast Tuesday.
However, impressive warm and moist advection noted by 850mb
southerly flow approaching 50 kts out of the Gulf of Mexico and
IVT approaching +4 standard deviations above the climo mean will
drive copious moisture northward. Where the column is cold enough,
this will manifest as moderate to heavy snow, sleet, and freezing
rain. With the surface low expected to track into the U.P. of MI,
heavy snow on D3 should be confined well NW of that track, and WPC probabilities for more than 4 inches of snow are currently just
20-30% and along the far northern MN border and the Arrowhead.
This snow is likely to be of the heavy and wet variety with low
SLR, so even a few inches could cause impacts, and more heavy snow
is likely into D4. Southeast of the snow area, a band of sleet and
freezing rain is likely, and while the NBM has backed off a bit on
its accretion, there is good consensus that a stripe of freezing
rain exceeding 0.1" is likely from northern WI across the L.P. of
MI and as far east as the Laurel Highlands of PA. Additional
freezing rain is likely into D4 as well, and it is possible that
notable impacts will occur from this freezing rain later this week.

Weiss

$$




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FOUS11 KWBC 271959
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
359 PM EDT Sun Mar 27 2022

Valid 00Z Mon Mar 28 2022 - 00Z Thu Mar 31 2022

...Great Lakes...
Day 1...

Multi-spoked upper low over Quebec will send one last vort max
across the eastern Great Lakes tonight into early Monday which
will help continue some lake bands into NW PA/Chautauqua Ridge in
NY, central NY, the Tug Hill Plateau, and into the Green Mountains
in Vermont. Up to a few inches of additional snow are expected and
WPC probabilities of at least 4 inches are generally low. Snowfall
will end by Monday afternoon as high pressure moves into the
region.


...California to the Rockies...
Days 1-3...

Water vapor shows a deep and wrapped-up upper low in the mature
phase just west of 130W and roughly due west of SFO, which is
forecast to weaken as it comes ashore central CA Monday
afternoon/evening and eventually it will become an open trough on
Tuesday across the Four Corners region. 130+ kt jet will slide
through Southern California on Monday, putting much of the Sierra
in the left front exit region. This will promote broad-scale lift
which will combine with a somewhat narrow surge of moisture (PW
anomalies around +1 to +2.5 sigma) and upslope flow into the
Transverse Range and central/southern Sierra. With the progressive
flow, precipitation will largely end by late Tuesday (end of day
2) west of the CO River as heights quickly rise. Snowfall will be
modest at higher elevations (snow levels roughly 6000ft) with
1-2ft possible from around 7-8000ft and higher. Some significant
pass level snow is likely as well, including Donner Pass.

As the system moves eastward Day 2 into 3, upper dynamics will be
less favorable given the weakening trough but still robust jet
streak. Moisture surge from the East Pacific will flow into the
Rockies from the southwest, supporting PW values of +1 to +2 sigma
in some locations. The system will be in a transition phase as a
northern stream vort max over Canada dives into the Dakotas,
helping to elongate the precipitation shield to the northwest into
Day 3. Higher terrain will capitalize on the available moisture
from Utah/Arizona into Colorado where high snow levels above
8000ft late Monday will lower to around 7000ft as colder air moves
in. WPC probabilities for more than 6 inches of snow are moderate
(40-70%) in the White Mountains of AZ, the San Juans, the Uintas,
the Wind Rivers, and much of the CO Rockies.


...Upper Midwest through the Mid-Atlantic...
Day 3...

System exiting the West/Rockies will transition to a new phase as
a northern stream vort max diving into the backside of the
positively-tilted and sheared upper trough helps spur cyclogenesis
over the central Plains Day 3. Upper jet will take on a classic
"S-shape" curve by late Wednesday with its anticyclonically-curved
northern branch arcing into the western Great Lakes and its
southern branch across the Northwest Gulf. Though the degree of phasing/interacting remains a bit uncertain as the features may
remain just offset in timing, guidance still supports a deepening
cyclone with broad warm advection to its east and overrunning
wintry precip to its northwest/north in colder air. Gulf moisture
will surge northward on 50-70kts flow bringing PW values of +1 to
+3 sigma and IVT around the 99th percentile into Michigan (higher
to the south) by the end of Day 3. Over Canada, a
quasi-banana-shaped high pressure will attempt to maintain cold
air closer to the Canadian border, especially northern MN into the
Arrowhead, but a mix of snow, sleet, and freezing rain is likely
across a large NW to SE swath from MN all the way through the
Great Lakes into parts of the interior Mid-Atlantic. Precipitation
types will likely be changeable through the event, so confidence
is low at this time range. Snow will likely be heavy and wet with
low SLRs, and ice accumulation may be more sensitive to
time-of-day as it is almost April. Through the end of Day 3 (00Z
31 March), WPC probabilities of at least 4 inches of snow are up
to about 40% near International Falls, MN and above 50% in the
Arrowhead, with more accumulation into Day 4. Freezing rain is
likely in a broad area with the potential for more than 0.1" over
parts of northern Wisconsin into Michigan. This may extend
southeastward into the Laurel Highlands of PA as well. WPC
probabilities of at least 0.25" ice exceed 10% over Lower Michigan.

Fracasso

$$




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FOUS11 KWBC 280833
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
433 AM EDT Mon Mar 28 2022

Valid 12Z Mon Mar 28 2022 - 12Z Thu Mar 31 2022

...California to the Rockies...
Days 1-2...

A deep closed low approaching CA this aftn will gradually weaken
as it lifts onshore and digs into the Great Basin by tonight. This
low is expected to fill into an open trough Tuesday aftn as it
moves into the southwest, but a persistent subtropical jet streak
arcing anticyclonically through the region will maintain upper
diffluence and aid in moist advection through mid-week. The
combination of the upper jet, and briefly enhanced warm/moist
advection will drive a modest AR onshore today, and PWs are
progged to reach near +2 standard deviations on both D1 and D2 for
CA and into the Four Corners region. The overlap of ascent and
moisture will lead to heavy snow, generally above 6000 ft or so in
the terrain across this area. On D1, this will manifest as heavy
snow in the Sierra and the San Bernadino/San Gabriel ranges of
southern CA where WPC probabilities for more than 6 inches are
moderate to high, and over 1 foot of snow is possible in the
higher terrain of the Sierra. This will also produce significant
accumulations at the important Sierra Passes, including Donner
Pass.

By D2 as the best forcing and moisture shift eastward, heavy snow
will overspread the terrain from the White Mountains of AZ east of
the Mogollon Rim, northward through the San Juans, CO Rockies
including the Front Range, Uintas, and Wind Rivers, where WPC
probabilities for more than 6 inches are as high as 70% in the San
Juans, and 30-50% elsewhere.


...Upper Midwest through the Mid-Atlantic...
Days 2-3...

Complex longwave trough development through the interaction of at
least 3 mid-level shortwaves will produce a long duration winter
weather event across portions of the Upper Midwest and Great
Lakes, with light wintry precipitation extending into the
Mid-Atlantic states. Guidance still features a wide variation in
possible outcomes for this event, but it is likely that two
surface lows will emerge out of the High Plains, with a leading
low moving from CO to MN on D2, and a secondary low emerging out
of OK and lifting towards MI on D3. The guidance has trended a bit
east once again tonight, indicating of a slower phasing of
mid-level energy, and is also suggesting the secondary low may be
the deeper system owing to a stronger shortwave and more
pronounced upper diffluence as a coupled jet structure develops.
Regardless of the exact evolution, moist advection out of the Gulf
of Mexico is progged to be intense on 850mb winds surging towards
50kts producing IVT exceeding +4 standard deviations according to
the NAEFS ensemble tables lifting into the Great Lakes. This deep
moisture combined with impressive deep layer ascent will spread
rounds of moderate to heavy precipitation northward, and a mix of
snow, sleet, and freezing rain is likely late Tuesday through
Thursday.

With the dual low structure producing significant uncertainty,
pinning down the locations of heaviest wintry precipitation is
challenging even for D2. However, utilizing the NBM and WSE
probabilities indicates for D2 the best chance for heavy snow will
be well north of the leading surface low, which is reflected by
WPC probabilities for 4+ inches as high as 30% along the MN/Canada international border. Potentially more significant on D2 will be
the freezing rain threat as a broad Canadian high pressure
retreats in advance of the surface low. With the intense WAA
surging northward ahead of this low, the warm nose will likely
reach the Canadian border, but wet bulb temps of 0C or less will
allow for a period of freezing rain which may accrete to more than
0.1" from central WI through the L.P. of MI and as far east as the
Laurel Highlands of PA.

For D3, the more significant low pressure is likely to emerge out
of the Southern Plains and lift quickly northeast while deepening.
There exists still considerable uncertainty into how this
secondary low will evolve, but an impressive theta-e ridge may
blossom into a TROWAL, supplying enhanced moisture and ascent into
a strengthening deformation axis across the Upper Midwest. The
NAM/RGEM are more aggressive with this deformation and displaced
west of the global consensus, so not preferred at this time, but
with yet another shortwave digging into the large gyre, many
solutions are still possible. CAA on the back side of this low
will also be more impressive, so the column should be cold enough
to support snow from eastern MN through the western U.P. of MI,
and if the deformation axis pivots in this area, heavy snowfall is
possible. At this time, WPC probabilities indicate a moderate risk
for more than 6 inches on D3, with moderate icing of 0.1" or more
possible across the eastern U.P. and northern L.P. of MI within
the better WAA.


Weiss

$$




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FOUS11 KWBC 282107
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
506 PM EDT Mon Mar 28 2022

Valid 00Z Tue Mar 29 2022 - 00Z Fri Apr 01 2022

...California to the Central/Southern Rockies...
Days 1-2...

A closed low will cross southern CA tonight before opening into a
wave over AZ early Tuesday, crossing the southern Rockies Tuesday
evening. Ahead of this main wave, a shortwave trough spins off the
low by this evening, reaching the southern Rockies late tonight.
An overlap of ascent from the low/trough and subtropical jet with
ample Pacific moisture streaming in ahead of the low will lead to
heavy mountain snow, with snow levels generally around 6000 ft
over CA/AZ and closer to 8000ft for CO/NM. Day 1 snow
probabilities are moderate for over 6" for the higher southern CA
ranges and the eastern side of the Sierra Nevada and ranges of
central NV (from cyclonic flow north of the low) and moderately
high for the ranges of southern UT/the Mogollon Rim of AZ/the
ranges of western CO.

Lee side cyclogenesis is over eastern CO tonight with enhanced
northeasterly flow into northeast CO/southeast WY Tuesday which
brings the CO Front Range and Sangre de Christos into moderate Day
2 snow probabilities over 6". There are some 2" Day 2 snow
probabilities onto the Palmer Divide/Raton Message.


...Northern Plains...Upper Midwest to the Central Appalachians and
into the New England...
Days 2-3...

Continued confidence in a rather complex longwave trough/low
development over the Upper Midwest by Thursday morning through the
interaction of 3 or 4 mid-level shortwave trough that will produce
a long duration winter weather event over the Upper Midwest and
Great Lakes Tuesday night through at least Thursday.

The leading shortwave trough from the closed low over southern CA
pushes northeast from the southern Rockies across the central
Plains Tuesday which interacts over the northern Plains with a
northern stream shortwave trough shifting southeast from the
Canadian Prairies Tuesday night. This directs the main wave from
the Southwest to shift east across the southern Plains Tuesday
night and should allow a closed low to form somewhere near IA
Wednesday that lifts to the Upper Midwest Wednesday night. Further reinforcement from the north on Thursday allows more development
as it likely lifts into Ontario. There is general agreement among
12Z guidance for this scenario though the 12Z GFS is a bit of an
outlier with forming the initial low earlier than the 12Z
ECMWF/UKMET/CMC which are in pretty good agreement synoptically
speaking. Regardless of the exact evolution, moist advection out
of the Gulf of Mexico is progged to be intense on 850mb winds
surging towards 50kts producing IVT exceeding +4 standard
deviations according to the NAEFS ensemble tables lifting into the
Great Lakes. This deep moisture combined with impressive deep
layer ascent will spread rounds of moderate to heavy precipitation
northward, and a mix of snow, sleet, and freezing rain is likely
late Tuesday through Wednesday night with wrap around snow
continuing Thursday potentially into Friday.

With the complex forcing/low structure producing uncertainty,
defining the likely narrow transition zones between wintry mixes
remains difficult. However, some refinement was able to be made
with this forecast. Day 2 snow probabilities for over 4" are 20 to
40% over the eastern border of the Dakotas and northern MN for
bands north of the initial surface low. Day 2 moderate ice
probabilities for over 0.1" extend east of the low across the
Upper Midwest along a low level boundary between the departing
Canadian high and warm air advection over north-central WI into
the western U.P. of MI and moderately high over the northern L.P.
of MI. Some low probabilities for over 0.1" are also over eastern
OH to west-central PA and western MD.

The main surface low shifts across MI Wednesday night into
Thursday with notable wrap around snow along a pivoting axis
expected. This brings high Day 3 snow probabilities for over 4"
south of Lake Superior (with moderate probabilities for 8") mainly
over the western U.P. with low probabilities stretching into
central WI. Day 3 ice probabilities over 0.1" are low to moderate
over the Upper Midwest and low over interior terrain of the
Northeast - the Adirondacks and Green/White Mtns.


Jackson

$$




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FOUS11 KWBC 290839
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
439 AM EDT Tue Mar 29 2022

Valid 12Z Tue Mar 29 2022 - 12Z Fri Apr 01 2022

...Central and Southern Rockies...
Day 1...

Closed mid-level low moving across CA this morning will gradually
weaken today into an open trough an d shift into the Four Corners
and then Central Plains by Wednesday morning. Confluent flow
downstream of this trough axis will continue to interact with a
subtropical Pacific jet streak to enhance moisture across the
region, with impressive ascent through height falls and LFQ
diffluence driving rounds of precipitation across the Southwest
and into the Central Rockies. Snow levels within the warm airmass
will generally be 6000-8000 ft, highest south, with significant
accumulations of snow likely above these levels. WPC probabilities
for more than 6 inches of snowfall are above 70% in the San Juans,
White Mountains of AZ, Sangre De Cristos, and many of the CO
Rockies, including the Front Range. Lighter accumulations are
likely in the Mogollon Rim, the Uinta Range, the higher terrain of
WY, and across the Raton Mesa and Palmer Divide.


...Northern Plains through the Upper Midwest, Great Lakes,
Mid-Atlantic, and New England...
Days 1-3...

Complex mid-level pattern development will produce a long duration
winter weather event during the next 3 days. While the most
significant impacts and accumulations are likely in the Upper
Midwest/Great Lakes, impactful winter weather is possible across a
large area from North Dakota through Pennsylvania and Maine.

The guidance has come into at least subtly better agreement
tonight that two distinct waves of low pressure will move from the
Plains through the Great Lakes, with the associated WAA out ahead
of the lows spreading wintry precipitation as far east as Maine.
The first wave will emerge out of the lee of the Rockies this aftn
and then shift rapidly northeast into the Great Lakes by Wednesday
morning. This low will deepen slightly as it lifts northeast in
response to modest height falls and strengthening LFQ upper
diffluence as an anticyclonically curved jet streak blossoms
downstream of the mid-level longwave trough axis. This forcing
will combine with increasing moist advection out of the Gulf of
Mexico, the result of which will be a swath of snow and sleet from
SD through MN and the western U.P, with moderate freezing rain
likely from eastern MN through WI, the L.P. of MI, and southeast
into the Laurel Highlands of PA. This event will be fast moving,
but anomalous moisture will still allow for heavy accumulation
potential of snow and freezing rain. WPC probabilities for more
than 4 inches of snow D1 as high as 20% in the Coteau des
Prairies, with freezing rain exceeding 0.1" most likely in
north-central WI and the L.P. of MI. As this system continues
northeast into D2, heavy snow on the NW side of the low will
continue in eastern SD and ND, and spread into the northern half
of MN including the Arrowhead, where WPC probabilities for 4+
inches reach above 40%. Additional freezing rain is likely into D2
across northern WI, the U.P., and the northern L.P. as well, with
storm total freezing rain possibly reaching 0.25" in a few
locations.

As wave 1 pulls away to the northeast and weakens, renewed
shortwave energy digging into the mean trough will combine with
intensifying upper diffluence within an coupled jet structure to
drive a stronger wave of low pressure from the Southern Plains
northeast into the Great Lakes D2-3. This low will likely produce
more significant wintry precipitation, as impressive theta-e
ridging rotates cyclonically into a TROWAL over the Upper Midwest,
and overlaps with a potent deformation axis that now has good
model support late D2 into D3. Where this axis pivots, snowfall
rates in excess of 1"/hr are likely despite modest SLRs as theta-e
lapse rates fall below 0C suggesting CSI potential. While the
models are in better agreement that this deformation will occur,
there are still significant longitudinal discrepancies, leading to
lowered confidence in where the heaviest snow will occur. There is
also concern that some of this area will be rain initially, and
the timing of the transition to snow as CAA strengthens behind the
low will have a significant impact on snowfall accumulations. At
this time the heaviest snow is most likely in a narrow corridor
from southwest WI through the western U.P. of MI where WPC
probabilities on D2 are as high as 70% for 4+ inches, with
additional heavy snow likely across the U.P. D3, first with this
heavy snow band, and later with impressive LES off Lake Superior.
Both the WSE and NBM have increased their snowfall for this area
D2-3, and locally 12 inches of snow is possible where the best
overlap of LES and banded snow occur.

Finally, as the entire system shifts northeast, WAA precipitation
into the terrain of VT/NH/ME may produce some light accumulations
of freezing rain, but WPC probabilities for more than 0.1" of
accretion are only 5-10%.


Weiss

$$




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FOUS11 KWBC 291959
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
357 PM EDT Tue Mar 29 2022

Valid 00Z Wed Mar 30 2022 - 00Z Sat Apr 02 2022

...Central and Southern Rockies...
Day 1...

Potent trough moving into the central High Plains this evening
will swing eastward into the Central Plains by Wednesday morning.
Confluent flow downstream of this trough axis will continue to
interact with a subtropical Pacific jet streak to enhance moisture
across the region, with impressive ascent through height falls and
LFQ diffluence driving rounds of precipitation into the Central
Rockies. Snow levels within the warm airmass will generally be
6000-8000 ft, highest south, with significant accumulations of
snow likely above these levels. Snow rates will drastically
decrease as upper-level forcing exits the region on Wednesday,
with lighter snow lingering into Wednesday night. WPC
probabilities for more than 6 inches of snowfall are above 70% in
the San Juans, Sangre De Cristos and Raton Mesa of NM, many of the
CO Rockies, including the Front Range. Lighter accumulations are
likely in the higher terrain of WY and across the Palmer Divide.


...Northern Plains through the Upper Midwest, Great Lakes, central
and northern Appalachians...
Days 1-3...

Complex mid-level pattern development will produce a long duration
winter weather event for the Great Lakes and Upper Midwest through
early Friday morning. Impactful winter weather is also possible
across a large area from the Dakotas through the central/northern
Appalachians.

Guidance continues to show relatively good agreement regarding the
two distinct shortwaves rounding the base of a larger scale trough
that will move from the Plains through the Great Lakes, with the
associated WAA out ahead of the trough spreading wintry
precipitation as far east as Maine. However, subtle differences
and recent trends lead to a decent amount of uncertainty remaining
even though the event will occur in less than 48 hours. The first
shortwave and associated moisture plume will emerge out of the
central Plains this evening and then shift rapidly northeast into
the Upper Midwest by Wednesday morning. An area of low pressure
will deepen slightly as it lifts northeast in response to modest
height falls and strengthening LFQ upper diffluence as an
anticyclonically curved jet streak blossoms downstream of the
mid-level longwave trough axis. This forcing will combine with
increasing moist advection out of the Gulf of Mexico, the result
of which will be a swath of snow and sleet from SD through MN and
the western U.P, with moderate freezing rain likely from eastern
MN through WI, the L.P. of MI, and southeast into the Laurel
Highlands of PA and western MD. This event will be fast moving,
but anomalous moisture will still allow for heavy accumulation
potential of snow and freezing rain. WPC probabilities for more
than 4 inches of snow D1 as high as 50-60% along the eastern ND
and SD border, with 20-30% probs extending across northern
Minnesota into the Arrowhead. Freezing rain exceeding 0.1" on D1
is most likely to occur in north-central WI and the L.P. of MI.
Additional freezing rain is likely into D2 across northern WI, the
U.P., and the northern L.P. as well, with storm total freezing
rain possibly reaching 0.25" in a few effected locations in MI.

As wave 1 pulls away to the northeast and weakens, renewed
shortwave energy digging into the mean trough will combine with
intensifying upper diffluence within an coupled jet structure to
drive a stronger wave of low pressure from the Southern Plains
northeast into the Great Lakes D2. This low will likely produce
more significant wintry precipitation, as impressive theta-e
ridging rotates cyclonically into a TROWAL over the Upper Midwest,
and overlaps with a potent deformation axis that now has good
model support. Where this axis pivots, snowfall rates in excess of
1"/hr are likely despite modest SLRs as theta-e lapse rates fall
below 0C suggesting CSI potential. While the models are in better
agreement that this deformation will occur, there still remains
significant longitudinal discrepancies, leading to lowered
confidence in where the heaviest snow will occur. There is also
concern that some of this area will be rain initially, and the
timing of the transition to snow as CAA strengthens behind the low
will have a significant impact on snowfall accumulations. At this
time the heaviest snow is most likely in a narrow corridor from
central WI through the western/central U.P. of MI. Most of the
heavy snow will occur during the overnight hours, which does
support accumulation within the heaviest snowbands even if warmer
ground temperatures/rain existed before the switch to snow. WPC
probabilities on D2 are as high as 80% for 4+ inches in the
western U.P., with additional heavy snow likely into D3 associated
with impressive LES off Lake Superior. Both the WSE and NBM have
maintained their snowfall for this area D2-3, and locally 12
inches of snow is possible where the best overlap of LES and
banded snow occur (most likely near and west of Marquette, MI).

Finally, on D3 as the aforementioned low pressure system exits
into SE Canada and a potent cold front swings through the
Northeast, lake effect snow showers and isolated snow squalls are
possible throughout the Great Lakes, Ohio Valley, and Northeast.
The typical upslope regions of western PA, NY, and the central
Appalachians will have the best chances for light accumulations.
Elsewhere, warm ground temperatures will make it difficult for
snow to accumulate, but visibility could still drop briefly under
the heaviest snow showers. The NAM and GFS snow squall parameter
shows this potential as lapse rates steepen during the day on
Friday.


Snell

$$




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FOUS11 KWBC 300811
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
411 AM EDT Wed Mar 30 2022

Valid 12Z Wed Mar 30 2022 - 12Z Sat Apr 02 2022

...Central Rockies...
Day 2...

A weakening shortwave moving onshore British Columbia on Wednesday
morning will drop southeast into the Central Rockies by Friday.
Modest height falls and PVA will accompany this feature as a
vorticity impulse swings through the base of the trough on D2. A
modest upper jet streak of 90-110 kts will accompany this feature
to enhance deep layer ascent through LFQ diffluence, but total
deep layer omega will remain transient. Moisture into the region
will increase Friday as noted by an increase in mid-level RH and
PWs rising to +0.5 standard deviations above the climo mean. The
modest ascent and rapid progression of the system keeps snowfall
accumulations relatively light, but WPC probabilities for more
than 6 inches are 20-40% in the Absarokas and Big Horns on D2.


...Upper Midwest, Great Lakes, Northeast...
Days 1-3...

Two low pressure waves will spread periods of wintry precipitation
during the next few days. The first is ongoing this morning as a
low pressure moves northeast out of Iowa and weakens. Pronounced
warm advection will continue out of the south spreading a moisture
plume into the Great Lakes and Upper Midwest. This WAA will
overrun cold surface air leftover from a retreating high,
producing an extended period of light to moderate freezing rain
from northern WI through the northern L.P. of MI and into the U.P.
The HREF suggests some areas may exceed 0.25" of freezing rain,
but this may be overdone due to runoff from periodic heavy rates,
and periods of drying which may limit total QPF in some areas. The
WSE and NBM are in pretty good agreement, resulting in a forecast
and PWPF that features probabilities for 0.1" above 30%, but less
than 5% chance for 0.25". Further to the NW where the column will
be colder, the guidance has become a bit more robust with an axis
of deformation snow pivoting from eastern SD and the Buffalo Ridge
northeast into the Arrowhead of MN and the western U.P. WPC
probabilities for more than 4 inches of snow have increased
slightly and are 20-30% on D1.

As this first low weakens, a secondary low emerging out of the
Southern Plains will deepen more rapidly in response to better
height falls within a large mid-level gyre, and accompanying upper
diffluence where the downstream jet streaks interact in a coupled
fashion. This should allow this secondary low to intensify much
more significantly as it lifts through the Great Lakes on D2.
Impressive WAA from the Gulf of Mexico will surge PWs to as high
as +3 standard deviations above the climo mean as 850mb flow
reaches above 60 kts. This will manifest as an impressive theta-e
ridging lifting into a TROWAL around this secondary low, and this
TROWAL may pivot along the NW flank in tandem with an impressive
axis of deformation. The guidance has come into much better
agreement that this will lead to a band of precipitation which
will change rapidly from rain to heavy snow Wednesday night into
Thursday. Although the antecedent conditions are less than
favorable for accumulation, snowfall rates will likely reach more
than 1"/hr as shown by the HREF probabilities and the WPC
prototype snowband tool. Dynamic cooling of the column during this
transition may allow changeover to occur faster than guidance, and
the WPC probabilities for more than 4 inches D1 and D2 above 20%
stretch from southeast MN through much of WI and into the
western/central U.P. Locally, probabilities are above 70%, and
storm total snowfall may reach 10 inches in the U.P. where
additional enhancement from Lake Superior is likely.

As the parent shortwave trough lifts into the Canadian Maritimes
on D3, CAA on impressive NW flow will likely produce moderate to
heavy upslope snow in the far northern reaches of New England and
Upstate New York. WPC probabilities for 4+ inches of snow are
5-10% in the Adirondacks, and 20-30% in the mountains of NH and ME.


...Great Lakes, Ohio Valley, Northeast...
Day 3...

A potent cold front racing across the area Thursday and Friday
will leave pronounced CAA in its wake, while an associated
mid-level closed low moving out of the Great Lakes and into New
England spins a vorticity lobe and height falls southward across
the region behind this front on Friday. The combination of
increasing instability due to steepening lapse rates and
impressive low-level fgen behind the front could produce scattered
to widespread heavy snow showers. Analysis also suggests an
increasing potential for at least isolated squalls embedded within
the more widespread snow showers. This is noted by an overlap in
guidance of high 0-2km fgen, 100-200 J/kg of SBCape, theta-e lapse
rates <0C/km, and a region of snow squall parameter values as high
as +3, focused across the Ohio Valley into the interior Northeast
on Friday. While this is outside the current high-res windows
which will likely pick up on the squall potential better, this
threat should continue to be monitored as the event evolves during
the next few days.

Weiss

$$




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FOUS11 KWBC 301953
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
353 PM EDT Wed Mar 30 2022

Valid 00Z Thu Mar 31 2022 - 00Z Sun Apr 03 2022

...Central Rockies...
Day 2...

Modest height falls and PVA will accompany an upper level
disturbance swinging through the base of the parent trough on Day
2. A modest upper jet streak of ~100 kts will promote deep layer
ascent thanks to diffluent flow within the jet streak's left front
quadrant, but total deep layer omega will remain fairly
progressive. Moisture into the region will increase Thursday night
and into Friday as noted by an increase in mid-level RH and PWs
rising up to 1+ standard deviations above the climo mean. Modest
ascent combined with rapid progression of the system keeps
snowfall accumulations relatively light, but WPC probabilities for
more than 6 inches are 20-50% in the Absorokas and Big Horns on D2
with the highest probabilities focused in the tallest peaks.


...Upper Midwest, Great Lakes, Northeast...
Days 1-3...

A strengthening storm system in the Great Lakes will produce a
swath of wintry weather extending from the Midwest to the Upper
Great Lakes tonight and into Thursday morning. This storm system
is working with ample amounts of Gulf of Mexico moisture that is
highlighted by a 3-4+ sigma PW anomaly over northern Michigan this
evening. A deformation zone is set to form over south-central
Wisconsin and into Michigan's U.P. where the axis of heavy snow is
likely to set up. 12Z HREF probabilities for snow fall rates

1"/hr range between 50-70% from southern and central Wisconsin on

north and east through the Green Bay area and into the eastern and
central U.P. between 06-12Z Thursday. As the low matures on its
northeast trajectory, colder air at low levels will run over Lake
Superior, prolonging the east-central U.P.'s bout of heavy snow
into the daytime hours on Thursday. Snowfall rates exceeding 1"/hr
may persist as late as 18Z Thursday before finally winding down as
the pressure gradient weakens due to the storm's progressive
movement. The U.P. of Michigan does contain the highest WPC
probabilities for >4" (>80% chance) while there is also up to a
60% chance for snow accumulations exceeding 8". It's worth
mentioning there is a 20-30% chance for snow accumulations
exceeding a foot, which lines up with the 13Z NBM's 90th
percentile which contains snow totals over a foot as well. Central
Wisconsin also has a chance for heavy snowfall accumulations with
a 40-60% chance of snow totals >4" for Day 1. The combination of
heavy snow and gusty winds may lead to near whiteout conditions
and drifting snow in affected areas.

The ongoing significant ice event in parts of northern Michigan
and Michigan's U.P. will transition to primarily rain by this
evening, but some lingering freezing rain/sleet may stick around
in the east-central U.P. before precipitation changes back to snow
later tonight.

...Great Lakes, Ohio Valley, Northeast...
Days 2-3...

An upper level shortwave diving south and east from northern
Minnesota tonight will deepen as it interacts with a small but
potent vorticity maximum tracking through Missouri Thursday
morning. As this trough races east, scattered snow showers will
envelope the Lower Great Lakes Thursday afternoon and into the
evening hours. The trough progresses towards the Northeast Friday
morning as lapse rates steepen to ~9C/km and an influx of low-mid
level moisture arrives, resultimg in widely scattered snow
showers. SBCAPE up to 100 J/kg may manifest over parts of
Pennsylvania and upstate New York and snow squall parameters of 3+
are shown on the 12Z GFS & 12Z NAM. This suggests the potential
snow snow squalls in parts of the interior Mid-Atlantic and
Northeast Friday morning and afternoon. It is worth noting that
the air-mass aloft is not in the same class of the one that
triggered intense snow squalls this past Monday. However, lapse
rates are steep and enough low level moisture is available to
support the potential for heavy bursts of snow and gusty winds
embedded within these snow showers, potentially leading to
dramatic drops in visibility and light accumulations.

As the lobe of vorticity tracks across the Northeast on Friday,
snow showers will also break out downwind of Lakes Erie and
Ontario, as well as in the favored upslope areas of the
Adirondacks and northern New England. Some of the highest
elevations may pick up as much as 4" in spots. Snow showers look
to wind down throughout the Northeast by Friday night.

Mullinax

$$




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FOUS11 KWBC 310833
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
432 AM EDT Thu Mar 31 2022

Valid 12Z Thu Mar 31 2022 - 12Z Sun Apr 03 2022

...Central Rockies...
Day 1...

Mid-level multi-vort shortwave will move southeastward out of
western Montana and the Pac NW today in the left front exit region
of a ~100kt jet streak. With a progressive flow and modest
moisture (precipitable water values just over average values for
late March/early April), snowfall will be on the light side
(generally under 6-8 inches at the higher elevations). WPC
probabilities for at least 4 inches of snow are moderate to high
over the Absarokas and Bighorns in Wyoming, and low to moderate
over western Colorado.


...Great Lakes and Northeast...
Days 1-2...

Mature cyclone wrapping up through Michigan this morning will
continue to lift into Canada today, drawing in colder air in its
wake over the Great Lakes. For the first part of Day 1,
deformation band snow will quickly accumulate over the eastern
U.P. of Michigan with rain changing to snow before ending over the
northwestern Lower Peninsula. A few additional inches of snow is
possible with lighter accumulations elsewhere as the precipitation
will quickly end just after 18Z.

As the main cyclone lifts away, a digging mid-level vort max will
slip through MN/WI this morning and into/through MI and the
Midwest overnight. This will help provide enough lift for
scattered snow showers this evening into the overnight hours from
Indiana eastward through Ohio. On Friday (Day 2), vort max will
swing through Pennsylvania where additional snow showers and
perhaps squalls are likely. Steep lapse rates, MUCAPE ~100 J/kg,
and sufficient (though modest at best) moisture provide the
ingredients for some snow squalls which may lead to difficult
travel at times due to quickly lowered visibility.

Upper trough moving through will also increase lake effect snows
for areas of the Chautauqua Ridge in western NY and into the Tug
Hill Plateau. A few inches of snow are likely in some areas, but
WPC probabilities of at least 4 inches are low (though some CAM
guidance showed more than 6 inches).


...Northwest...
Days 1-3...

Departing mid-level shortwave and modest jet streak will spread
light snow over the Cascades and northwestern Montana Day 1 before
a break in the precipitation as upper ridging moves in briefly
overnight tonight. On Day 2, shortwave and surface cold front will
move into WA/OR but with limited moisture. Again only light snow
is forecast for much of the region with snow levels down to around
3000-4000 ft. This snow will cross into Day 3 for northern Idaho
and northwestern Montana where several inches of snow are possible
for the higher elevations. Snow levels will be around 2000 ft.


For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.


Fracasso


~~~ Key Messages for March 31 - April 1 Snow Squalls ~~~
* A strong cold front will push through the Ohio Valley today and
the Northeast tonight.
* Scattered snow squalls may develop and move over the Ohio
Valley/Great Lakes region tonight. Snow squalls are likely during
the day on Friday from the central Appalachians and Lower Great
lakes toward the interior Northeast and Mid-Atlantic.
* Intense but brief snowfall within these snow squalls can rapidly
reduce visibility and lead to dangerous driving conditions,
particularly on high-speed roadways.
* Little to no accumulation is expected outside of the higher
terrain, but slick spots may develop on bridges and overpasses.

$$




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FOUS11 KWBC 311852
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
252 PM EDT Thu Mar 31 2022

Valid 00Z Fri Apr 01 2022 - 00Z Mon Apr 04 2022

...Central Rockies...
Day 1...

Shortwave trough moving onshore the Pacific Northwest today dives
southeast and deepens as it swings through the Central Rockies
through tonight. Height falls and forcing for ascent provided by
the left exit region of the 100 kt jet streak will lead to modest
snow amounts for the Absarokas and Bighorns in WY and western
Colorado. WPC probabilities for 4 inches are slight to moderate
through 12Z Friday before tapering off quickly during the day
Friday.


...Great Lakes and Northeast...
Day 1...

Digging mid-level vort max currently over MN/WI this afternoon
swings through the Great Lakes this evening and across the
Mid-Atlantic and Northeast Friday. This feature will provide the
necessary lift for isolated/scattered snow showers. Some of these
showers could be vigorous and lead to snow squalls thanks to
steepened lapse rates, modest MUCAPEs of a few hundred J/kg, and
sufficient moisture in place. Downwind of Lake Erie and Ontario
are likely to pick up a few inches (slight/moderate signal for
2"+) while the favored upslope region in WV has 40-60 percent
probabilities for 1-2".


...Northwest...
Days 2-3...

Another round of unsettled weather comes to the Pacific Northwest
during the Day 2/3 period as a shortwave trough moves through.
Increased moisture and broad forcing for ascent will lead to
snowfall accumulation above 4-5kft and the latest WPC
probabilities show moderate to high probabilities for 4" over the
WA Cascades then slight/moderate probabilities across northern
Idaho and northwest Montana.



For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.


Taylor


~~~ Key Messages for March 31 - April 1 Snow Squalls ~~~

-A strong cold front will push through Northeast tonight while
colder temperatures filter into the Great Lakes and Ohio Valley
this evening.

-Scattered snow squalls may develop and move over the Ohio
Valley/Great Lakes region tonight. Snow squalls are likely during
the day on Friday from the central Appalachians and Lower Great
Lakes toward the interior Northeast and Mid-Atlantic.

-Intense but brief snowfall within these snow squalls can rapidly
reduce visibility and lead to dangerous driving conditions,
particularly on high-speed roadways.

-Little to no accumulation is expected outside of the higher
terrain, but slick spots may develop on bridges and overpasses.



$$




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FOUS11 KWBC 010832
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
431 AM EDT Fri Apr 01 2022

Valid 12Z Fri Apr 01 2022 - 12Z Mon Apr 04 2022

...Great Lakes and Northeast...
Day 1...

Mid-level vort max behind the surface cold front now moving off
the East Coast will move through the Pennsylvania this afternoon
atop a surface trough extending southwestward from the parent low.
This will provide the necessary lift for isolated/scattered snow
showers, some of which could be vigorous and lead to snow squalls.
Steepened lapse rates, modest MUCAPEs of a few hundred J/kg, and
sufficient moisture in place support their development though
accumulation may be limited due to marginal surface temperatures.
Areas downwind of Lakes Erie and Ontario are likely to pick up a
few inches of snow (especially into the Tug Hill) with westerly to northwesterly flow during the day. Additional accumulations are
expected over the Adirondacks and Green/White Mountains in VT/NH
as the upper trough swings through, with probabilities of at least
4 inches confined to higher elevations.


...Corn Belt...
Days 1-3...

Two systems will likely affect the region over the next three
days. The first will be at the very end of Day 1 into Day 2 (early
Sat) as a mid-level shortwave moves through Iowa. At the surface,
an area of low pressure will exit Colorado and slip eastward as a
brief surge in precipitable water noses into eastern Iowa and
southern Wisconsin. Temperatures at the surface will be marginal,
near and maybe just above 32F, but CAM guidance suggests a focused
area of frontogenesis over the area around 12Z Sat with
appreciable lift into the DGZ. WPC snowband tool shows the
possibility of >1"/hr rates around daybreak which could accumulate
a few inches (note WPC's WSE and HREF max snow are both around
6").

Next system will be on Sunday evening into early Monday. Model
spread is large with this system, so took a conservative/blended
approach which yielded a light amount of snow farther north
(northern WI) but only around 1-2".


...Northwest...
Days 1-3...

A weak system will move through the area Day 1 with snow levels
around 4000ft before falling a bit on Saturday behind the front.
By Day 3, strong/extended jet (160 kts) across the Pacific will
aim into the WA/OR coast with the precipitable water surge focused
over northern California into Oregon. Still, PW values around +1
will push into the Cascades ahead of a lead wave and then a
subsequent more developed system (into Day 4). WSW flow will
capitalize on upslope into the Olympics and Washington Cascades
where more than a foot of snow is expected on Day 3. Lesser
amounts are expected into Oregon where snow levels will be higher.


...CO Rockies...
Day 3...

Weak upper trough and surface cold front will lead to an increase
in snow over higher elevations of Colorado Day 3, aided by upslope
flow as an area of high pressure sinks southeastward over the
Plains. Several inches are expected into the Sawatch Range into
the Sangre de Cristos.


For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.


Fracasso


~~~ Key Messages for March 31 - April 1 Snow Squalls ~~~

-A strong cold front will push off the East Coast this morning as
colder temperatures filter into the region.

-Snow showers and squalls are likely today from the central
Appalachians and Lower Great Lakes into the interior Northeast and Mid-Atlantic.

-Intense but brief snowfall within these snow squalls can rapidly
reduce visibility and lead to dangerous driving conditions,
particularly on high-speed roadways.

-Little to no accumulation is expected outside of the higher
terrain, but slick spots may develop on bridges and overpasses.



$$




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FOUS11 KWBC 012027
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
425 PM EDT Fri Apr 01 2022

Valid 00Z Sat Apr 02 2022 - 00Z Tue Apr 05 2022

...Eastern Great Lakes and Northeast...
Days 1-2...

An amplified upper level shortwave and its associated surface
reflection will continue to move across the Northeast this
evening. In addition to some wraparound precipitation spreading
across the U.S.-Canada border into northern New England, lake
effect showers are expected to continue into the evening hours.
Snow is expected to diminish as a shortwave ridge shifts east
across the region tonight. Overall, additional heavy
accumulations tonight into early tomorrow are not expected.

After a brief dry period, precipitation is expected to return the
region as another amplified shortwave crosses the region Saturday
night into Sunday. Across Upstate New York, thermal profiles
support snow initially before changing to a rain/snow mix,
especially across the lower elevations. Again, widespread heavy
accumulations are not expected.

...Corn Belt...
Days 1-3...

Two systems will likely affect the region over the next three
days. The first will develop tonight as a mid-level shortwave
moves through Iowa. At the surface, an area of low pressure will
exit Colorado and slip eastward as a brief surge in precipitable
water noses into eastern Iowa and southern Wisconsin. Temperatures
at the surface will be marginal, near and maybe just above 32F,
but CAM guidance continue to suggest a focused area of
frontogenesis over the area around 12Z Sat with appreciable lift
into the DGZ. WPC snowband tool shows the possibility of >1
inch/hr rates around daybreak which could accumulate a few inches
from northeastern Iowa into southern Wisconsin. WPC probabilities
have shown a small increase in the chances for accumulations of 2
inches or more across this area.

The next system will be on Sunday evening into early Monday.
Probabilities for accumulating snow have increased with the latest
run across portions of Wisconsin into Lower Michigan, however
model spread is still significant with this system, limiting
probabilities and forecast confidence.


...Northwest...
Days 1-3...

A weak system will move through the area tonight with snow levels
around 4000ft before falling a bit on Saturday behind the front.
By Sunday night, a strong/extended jet (160 kts) across the
Pacific will aim into the Northwest coast with a significant
moisture flux reaching into western Washington/Oregon.
West-southwest flow will capitalize on upslope into the Olympics
and Washington Cascades where widespread accumulations of a foot
or more are likely, with multiple feet possible across the higher
peaks. Lesser amounts are expected into Oregon where snow levels
will be higher.


...Colorado/New Mexico Rockies...
Day 3...

Weak upper trough and surface cold front will lead to an increase
in snow over higher elevations of Colorado on Sunday, aided by
upslope flow as an area of high pressure sinks southeastward over
the Plains. At least a few inches of snow can be expected across
the higher elevations of the central Colorado and far northern New
Mexico ranges.


For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.


Pereira/Fracasso




$$




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FOUS11 KWBC 020658
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
256 AM EDT Sat Apr 02 2022

Valid 12Z Sat Apr 02 2022 - 12Z Tue Apr 05 2022

...Eastern Great Lakes and Northeast...
Day 2...

Amplified shortwave will move through the region late tonight
through Sunday in tandem with an area of low pressure along the
NY/PA border. Snow in the morning will change to a rain/snow mix
over many areas during the afternoon with generally light amounts.
Some higher totals near 4 inches are possible in the Catskills and
portions of the Green Mountains. WPC probabilities for more than 4
inches are low.

...Corn Belt/Upper Midwest/Great Lakes...
Days 1-3...

Area of low pressure will skirt through the region this morning
with a burst of snow before zipping eastward. Brief surge in
precipitable water along with a focused area of frontogenesis with
sufficient lift into the DGZ will squeeze out a couple inches or
so more of snow after 12Z this morning along the WI/IL border with
another inch or two across northern Lower Michigan. Next system
(currently moving through the Pacific Northwest) will quickly move
into the High Plains overnight and into the Upper Midwest/Corn
Belt Sunday into Sunday night. An inch of two of snow is possible
with this system, focused over northern WI into Lower Michigan.
Three day totals may exceed 4 inches there.

...Northwest...
Days 2-3...

By Sunday night, a strong/extended jet (160 kts) across most of
the Pacific will aim into the Northwest coast with a significant
moisture flux reaching into western Washington/Oregon.
West-southwest flow will capitalize on upslope into the Olympics
and Washington Cascades where widespread accumulations of a foot
or more are likely and multiple feet are possible across the
higher peaks. Significant accumulations are possible at some
passes as well. Lesser amounts are expected into Oregon Day 2
where snow levels will be higher. By the end of Day 3, snow levels
will drop to around 2000ft across WA as the precipitation only
starts to wind down. Accumulations over the Oregon Cascades will
increase markedly on Monday. Also on Day 3, as the trough or
closed low and jet move east of the Divide, snow will spread
across Idaho/western Montana and into Wyoming with several inches
likely above 6000ft but snow levels will lower quickly Tuesday
morning to most valley floor locations.


...Colorado/New Mexico Rockies...
Day 2...

Weak upper trough and surface cold front will lead to an increase
in snow over higher elevations of Colorado on Sunday, aided by
upslope flow as a small area of high pressure sinks southeastward
over the Plains. At least a few inches of snow can be expected
across the higher elevations of the central Colorado and far
northern New Mexico ranges.


For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.


Fracasso/Pereira




$$




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FOUS11 KWBC 021941
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
339 PM EDT Sat Apr 02 2022

Valid 00Z Sun Apr 03 2022 - 00Z Wed Apr 06 2022

...Eastern Great Lakes and Northeast...
Day 1...

Amplified shortwave will move through the region late tonight
through Sunday in tandem with an area of low pressure along the
NY/PA border. Snow in the morning will change to a rain/snow mix
over many areas during the afternoon, with generally light
amounts. Some higher totals near 4 inches are possible, but will
likely be mostly confined to the higher elevations of the
Catskills.

...Corn Belt/Upper Midwest/Great Lakes...
Days 1-3...

A shortwave currently moving through the the northern Rockies will
quickly move into the High Plains overnight and into the Upper
Midwest/Corn Belt Sunday into Sunday night. An inch or two of snow
is possible over portions of western to central North Dakota, into
northeastern South Dakota on Sunday, before shifting farther east
into Wisconsin and Lower Michigan Sunday night into Monday.

...Northwest to the northern Rockies...
Days 1-3...

By Sunday night, a strong/extended jet (160 kts) across most of
the Pacific will aim into the Northwest coast with a significant
moisture flux reaching into western Washington/Oregon.
West-southwest flow will capitalize on upslope into the Olympics
and Washington Cascades where widespread accumulations of a foot
or more are likely and multiple feet are possible across the
higher peaks. Significant accumulations are possible at some
passes as well. Along the Oregon Cascades, lesser amounts are
expected into early Monday where snow levels will be higher. By
early Tuesday, snow levels will drop to around 2000ft across WA as
the precipitation only starts to wind down. Accumulations over the
Oregon Cascades will increase markedly on Monday. Also on Day 3,
as the trough or closed low and jet move east of the Divide, snow
will spread across Idaho/western Montana and into Wyoming with
several inches likely above 6000ft, but snow levels will lower
quickly Tuesday morning to most valley floor locations.


...Colorado/New Mexico Rockies...
Days 1-2...

Weak upper trough and surface cold front will lead to an increase
in snow over higher elevations of Colorado on Sunday, aided by
upslope flow as a small area of high pressure sinks southeastward
over the Plains. At least a few inches of snow can be expected
across the higher elevations of the central Colorado and far
northern New Mexico ranges.


For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.


Pereira/Fracasso




$$




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FOUS11 KWBC 030737
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
336 AM EDT Sun Apr 03 2022

Valid 12Z Sun Apr 03 2022 - 12Z Wed Apr 06 2022

...Northeast...
Day 1...

Amplified shortwave will move through the region today in tandem
with a lead area of low pressure along the NY/PA border. Snow in
the morning will change to a rain/snow mix over many areas during
the afternoon as a secondary area of low pressure develops off the
NJ coast by the afternoon. Generally light amounts are expected,
though some higher totals around 4 inches are possible in the
higher elevations of the Catskills.

...Upper Midwest/Great Lakes...
Days 1-3...

A shortwave and organizing surface low over North Dakota this
morning will quickly move into the Upper Midwest/Corn Belt this afternoon/evening. A disjointed stripe of an inch or two of snow
is possible over portions of central southern North Dakota
east-southeastward into Wisconsin and Lower Michigan tonight into
Monday. Thermal profiles will be marginal over southern Wisconsin
where potential exists for several inches of snow as an area of
FGEN moves across the area, promoting lift into the DGZ for a
brief window Monday morning. WPC snowband tool does show a few
members with 1"/hr rates for a time. Otherwise, WPC probabilities
for at least 4 inches of snow are low but focused over
southern/southeastern Wisconsin.

On Day 3, front associated with the Pac NW event (section below)
will move into the northern Plains. Mid-level shortwave will dig
and close off over the Dakotas into Minnesota late Tuesday into
Wednesday. Stacked system will occlude and wrap up with a surge in
moisture from the south (not quite the Gulf) on the warm conveyor
belt into the colder air mostly near the Canadian border. A few
inches of snow are likely for at least the Arrowhead of Minnesota
where temperatures should be cold enough for snow. WPC
probabilities for at least 4 inches of snow are low at this time.


...Northwest to the northern Rockies...
Days 1-3...

Lead/weak system will push into western Washington this morning,
but by tonight, the strong/extended jet (~170 kts) across most of
the Pacific will aim into the Northwest coast with a significant
moisture flux reaching into western Washington/Oregon.
Precipitable water values will reach +1 to +2 sigma Monday ahead
of a cold front that will move through the region as a west-east
stretched vort max streams eastward. West-southwest flow will
capitalize on upslope into the Olympics and Washington Cascades
where widespread accumulations of 1-2+ ft are likely and multiple
feet are possible across the higher peaks. Significant
accumulations are possible at some passes as well. Along the
Oregon Cascades, lesser amounts are expected into early Monday
when snow levels will be higher. By early Tuesday, snow levels
will drop to around 2000ft across WA as the precipitation only
starts to wind down. Accumulations over the Oregon Cascades will
increase markedly on Monday. High pressure will move in late
Tuesday, helping to push the precipitation eastward. Snow will
spread across Idaho/western Montana Monday and into Wyoming
Tuesday with several inches likely above 6000ft. Snow levels will
lower quickly Tuesday morning to most valley floor locations but
with little accumulation. Snow will ease and wind down on Day 3 as
the front sinks southward and eastward.


...Colorado/New Mexico Rockies...
Day 1...

Weak upper trough and surface cold front will lead to an increase
in snow over higher elevations of Colorado today, aided by upslope
flow as a small area of high pressure sinks southeastward over the
Plains. At least a few inches of snow can be expected across the
higher elevations of the central Colorado and far northern New
Mexico ranges.


For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.


Fracasso




$$




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FOUS11 KWBC 032007
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
405 PM EDT Sun Apr 03 2022

Valid 00Z Mon Apr 04 2022 - 00Z Thu Apr 07 2022

...Upper Midwest/Great Lakes...
Days 1-3...

A vigorous shortwave trough swinging through the Midwest this
afternoon will direct a wave of low pressure towards the Great
Lakes tonight. Upper level diffluence ahead of the trough and a
strengthening 850-700mb FGEN band support a swath of precipitation
across Wisconsin tonight and into Michigan by Monday morning. Area
averaged model soundings indicate wet bulb temperatures at low-mid
levels would be subfreezing and dynamic cooling as a result of the strengthening vertical ascent will allow for periods of snow to
ensue. The big question remains boundary layers temps. In areas
where forcing is strongest, snowfall rates up to 1"/hr can help
surface temps fall close to freezing with light accumulations
possible. Latest WPC probabilities of >4" are highest in
north-central Wisconsin, but even those probabilities top out at
20%, suggesting perhaps some localized spots could surpass 4", but
the majority of snowfall totals should fall short of 4". Meanwhile
in southern Wisconsin, northern Illinois, and southern Michigan,
boundary layer temps in the lowest 500-1,000 feet appear to be
above freezing. In addition, a 700-300mb layer dry slot will
quickly work its way east with the progressive shortwave, making
any window for accumulating snow on the matter of only a few
hours. Expecting less accumulations south of I-96 as a result,
although some reduced visibilities from a brief burst of snow
could still occur.

On Day 3, an amplifying upper low diving southeast from southern
Canada will spawn a new wave of low pressure in the northern High
Plains Tuesday morning. Strong WAA and PVA out ahead of the trough
will give way to periods of snow across North Dakota and northern
Minnesota. The area with the best odds for snowfall totals
surpassing 4" is the Minnesota Arrowhead where the additional
snowfall enhancement, thanks to onshore flow off Lake Superior,
where WPC probabilities are up to 40%. How much snow accumulates
in parts of North Dakota and northern Minnesota remains unclear
due to lingering model spread and uncertainty in how cold the
boundary layer is in these areas. Farther west, as colder air
spills down into Montana, northern Wyoming, and the Black Hills,
upslope flow may cause periods of heavy snow to breakout on
Tuesday. The Black Hills have a 50-70% chance for snowfall totals

4" while the Big Horns of Wyoming and the Big Snowy and Little

Belt mountains of Montana are currently pegged at 20-40% for
similar snowfall totals.


...Northwest to the northern Rockies...
Days 1-3...

Tonight, the nose of a roaring 250mb jet (~170 kts, ~3-4+ sigma)
is helping to usher in an atmospheric river across the Northwest
tonight. Substantial amounts of Pacific moisture (~2+ sigma) will
move ashore with strong westerlies at mid-levels also causing
enhanced precipitation rates in the Olympics, Cascades, and
eventually the northern Rockies Monday morning. The brisk onshore
and uplsloping flow pattern over these regions will persist
through Tuesday morning, making for a long duration heavy snow
event. Snowfall will be measured in feet in the Olympics,
Cascades, Sawtooths, and Bitterroots while farther south and east,
the Tetons and Wind River Ranges of Wyoming could also pick up
over a foot of snow. Impacts to travel, particularly highways in
the higher elevations, could be subjected to very poor
visibilities and snow covered roads, making travel dangerous in
some cases. In fact, widespread High Wind Watches and Warnings
have been posted throughout much of the Pacific Northwest and
Northern Rockies through late Tuesday, so any snowfall could lead
to near whiteout conditions at times. Snowfall rates gradually
taper off late Tuesday throughout the Pacific Northwest and
northern Rockies as drier air filters on the backside of an
emerging upper trough in southern Canada and high pressure builds
in throughout the Northwest on Wednesday.


...Colorado/New Mexico Rockies...
Days 1-2...

A weak upper trough and upslope low level flow will foster a
favorable environment for snow in the southern Colorado Rockies
and far northern New Mexico Rockies tonight and into Monday
morning. Some of the highest elevations of southern Colorado could
receive over 8" (WPC probabilities of as high as 30% in spots). As
that upper trough leaves, the intensifying system in the northern
High Plains early Tuesday morning will direct a cold front south
through the Rockies. This, along with strong upsloping flow from
the intense jet streak over the Northwest, allows for another
round of snow to envelope the Colorado Rockies. This time around
through, it is the central and northern Colorado Rockies that have
the better odds of receiving heavy snow (50-70% chance for >4" of
snow in the higher elevations). Strong winds in these impacted
areas may cause reduced visibilities and treacherous travel
conditions on Tuesday.


For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.


Mullinax




$$




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FOUS11 KWBC 040841
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
439 AM EDT Mon Apr 04 2022

Valid 12Z Mon Apr 04 2022 - 12Z Thu Apr 07 2022

...Northwest to the northern/central Rockies...
Days 1-2...

Strong, powerful, and elongated 170 kt jet will push into WA/OR
today as a strong cold front moves through the region.
Precipitable water surge will be short-lived in the progressive
flow, peaking around +1 to +2.5 sigma today then dropping to below
climo values Day 2. However, onshore flow will continue as a
trailing mid-level vort max swings through Washington early
Tuesday. Upslope will be robust into the Cascades where total
amounts well over a foot will be common, including at some passes.
Strong winds will create blowing snow and reduced visibility. Snow
levels around 4000 ft this morning will drop to below 2000 ft this evening/overnight as much colder air moves in. Strong westerly
flow will carry significant moisture east of the Cascades as well,
focusing on the mountains in Idaho and western Montana as the
front rapidly moves eastward today. Again, blowing snow will be
common after the front passes; steep lapse rates will support
squally snow showers after the main area of precip passes. Snow
will spread into Wyoming by this afternoon where significant
accumulations are also expected over the Tetons, Absarokas, and
Wind River Ranges. Lighter snow will fall into Colorado by Day 2
with several inches in the higher terrain where snow levels will
be much higher than in the Northwest.

WPC probabilities for at least 12 inches of snow are high for
elevations above around 2500 ft in the Cascades and are high for
at least 6 inches of snow above around 5000 ft in Idaho/Montana
and 5000-7000ft into Wyoming.


...Northern Plains/Upper Midwest/Western Great Lakes...
Days 1-3...

Weakening surface low this morning will spread generally light
snow across Wisconsin into Lower Michigan with accumulations under
a few inches, focused in the 12-18Z window. WPC probabilities for
at least 4 inches of snow are less than 10 percent.

On Day 2, western system will move through the High Plains as the
mid-level vort digs into the Dakotas and closes off. Triple point
low will take over as the main surface low on Tuesday as the
system becomes stacked by Day 3, allowing moisture from the south
to stream northward on the WCB. Temperatures will be marginal over
much of the area except for toward the Canadian border and
especially over the Arrowhead of Minnesota. Easterly flow will
enhance lake-enduced convergence along the North Shore with
upslope into the higher terrain where several inches of snow are
possible Days 2-3. To the west, wobbling low centers will
generally favor northwesterly flow into the Black Hills where
upslope there will promote moderate snow totals on Day 3. WPC
probabilities of at least 4 inches of snow are low to moderate
over portions of the Arrowhead and moderate to high over the Black
Hills.


For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.

Fracasso





$$




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FOUS11 KWBC 041921
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
320 PM EDT Mon Apr 04 2022

Valid 00Z Tue Apr 05 2022 - 00Z Fri Apr 08 2022

...Northwest to the northern/central Rockies...
Days 1-2...

Elongated and powerful 170+kt Pacific jet streak will extend
onshore the Pacific Northwest tonight before driving eastward into
the Northern Rockies Tuesday. This feature will be accompanied by
strongly confluent 500mb flow and zonal 850-700mb winds, all
acting to enhance moisture as an atmospheric river with IVT near
750kg/m/s surges onshore. A cold front well ahead of this moderate
AR will help drive snow levels down to as low as 1500 ft in the
Cascades and Northern Rockies during the period of heaviest snow,
with only slow recovery towards 2500 ft as the snow intensity
wanes and becomes more showery late D1 into D2. With high
moisture, impressive deep layer ascent, enhanced upslope flow on
orthogonal low-level winds, and relatively higher SLR in the cold
column, heavy snow is likely for much of the terrain Monday night
and Tuesday. Significant moisture lifting into the Cascades could
produce in excess of 3 feet in the higher terrain, and WPC
probabilities for more than 12 inches on D1 for the WA Cascades
and Olympics where the heaviest accumulations are likely.
Probabilities for more than 12 inches are moderate elsewhere in
the OR Cascades and further east including parts of the Northern
Rockies, Absarokas, and Wind Rivers. Additionally, with the very
low snow levels, heavy snowfall is likely as the important Cascade
Passes including Stevens and Snoqualmie.


...Northern Plains/Upper Midwest/Western Great Lakes...
Days 1-3...

A shortwave dropping out of Alberta will race southeast into the
Northern Plains before stalling in response to being captured into
a slow moving and deep closed low over the region. This low will
spin slowly over the area D2-3, potentially retrograding at times,
as reinforcing shortwaves amplify the trough to as low as -3
standard deviations with respect to 5H heights according to the
NAEFS ensemble tables. Beneath this feature, a weak surface low
will drift from MN to WI and finally MI by the end of D3. Although
this low will be vertically stacked, moist advection out ahead of
it will be impressive as low-level flow out of the Gulf of Mexico
surges PWs to +1.5 standard deviations within the warm advection,
with some of the theta-e ridging trying to wrap cyclonically into
a TROWAL D2. Although forcing and moisture begin to wane late
Wednesday into Thursday, the guidance has become more aggressive
with deformation axis development NW of the low across the
Northern Plains D3, which could enhance snowfall. Modest total
forcing should somewhat limit snowfall accumulations within this
deformation, but increasing SLRs and some upslope into higher
elevations on northerly flow could lead to moderate to heavy
accumulations.

WPC probabilities on day 1 are minimal as the pattern becomes more
favorable for heavy snow late in the forecast period. However,
both D2 and D3, WPC probabilities for 4+ inches of snow reach as
high as 70% across the Black Hills, the Coteau des Prairies, and
the Arrowhead of MN due to terrain influences and upslope flow,
with moisture off Lake Superior adding to snow potential in the
Arrowhead. Locally, more than 8 inches of snow is possible over
the 2 days in the Arrowhead and highest terrain of the Black
Hills. By D3, some heavier snowfall is likely south of Lake
Superior near the Bayfields Peninsula due to Lake Enhancement.


For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.

Weiss





$$




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FOUS11 KWBC 050747
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
346 AM EDT Tue Apr 05 2022

Valid 12Z Tue Apr 05 2022 - 12Z Fri Apr 08 2022

...Northwest to the northern/central Rockies...
Day 1...

Strong jet that carried a cold front quickly through the Northwest
yesterday will weaken and lift northeastward as upper ridging
builds into the PacNW this afternoon/evening. Any precipitation
early in the day will end by then as high pressure builds in off
the northeastern Pacific. Snowfall will still be heavy over the
northern Cascades just after 12Z today where an additional 6+
inches of snow is likely. Downstream, some additional amounts over
four inches are likely into the Bitterroots and western Montana as
well as western Wyoming and Colorado as forcing wanes by evening.


...Northern Plains/Upper Midwest/Western Great Lakes...
Days 1-3...

Closed low forming over southwestern Saskatchewan this morning
will merge into the sheared vort out of the northern Rockies today
spurring cyclogenesis into Minnesota today. By Wednesday, another
smaller closed low over northern Ontario will rotate into the
western side of the deepening closed low over Minnesota as the
system becomes stacked up to jet level. The multiple axes of
vorticity will result in a deformed ellipse at 500mb with
different foci for lift. On Day 3, the expanding upper low will
sink southeastward into the eastern Great Lakes.

Life cycle of the system through the period will start with strong
PVA and jet expansion into the Upper Midwest and Great Lakes with
an increase in moisture from the southwest back to northeast Texas
(PW anomalies +1 to +1.5 sigma). WCB will bring sufficient
moisture to the Arrowhead where temperatures will be marginally
cold for snow, with lower amounts over northern Minnesota. By Day
2, upper pattern will amplify as the surface low wobbles eastward
but the cold front swings into the eastern Great Lakes. This will
stretch the moisture plume that taps the Gulf (+1 to +2 sigma) but
displaced into the Northeast. On the backside of the broad
circulation, second vort max (old upper low) will provide
additional lift combined with upslope flow into the Black Hills
for several inches of snow. With the wrapped occlusion over the
Great Lakes, TROWAL development will try to ensue before the
system overturns and a new area of low pressure forms along the
Mid-Atlantic coast. On Day 3, leftover parent low will drift into
the Midwest with northerly to northeasterly flow over
Michigan/Wisconsin supporting lake-enhanced snow and a rather
expansive area of light snow beneath the cold pool.

WPC probabilities for at least four inches of snow are moderate
over the Arrowhead of Minnesota and low over parts of the rest of
northern Minnesota. Probabilities increase by Day 2 everywhere as
the system reaches maturity -- moderate to high over the
Arrowhead, low over northern Minnesota, and moderate over the
Black Hills. On Day 3, moderate to high probabilities of at least
four inches of snow are focused over the Gogebic Range across
northern Wisconsin into the U.P. of Michigan. Three-day totals of
over eight inches are low to moderate over similar areas.


For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.

Fracasso

$$




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FOUS11 KWBC 051955
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
354 PM EDT Tue Apr 05 2022

Valid 00Z Wed Apr 06 2022 - 00Z Sat Apr 09 2022

...Pacific Northwest...
Day 3...

A potent shortwave digging into the Pacific Northwest Friday
morning will be preceded by confluent mid-level flow and
pronounced WAA to surge moisture into OR/WA on D3. PW anomalies
Friday morning reach above +1.5 standard deviations above the
climo mean, into which a surface front, height falls, and modest
LFQ diffluence will provide ascent to expand a swath of
precipitation beginning Friday morning. Snow levels within the WAA
rise as high as 6000-7000ft, but will drop though Friday night to
as low as 3000 ft causing rain to change to snow even at some of
the passes. WPC probabilities are moderate for more than 4 inches
in the WA Cascades D3, with some light accumulations possible at
the passes. More snow is likely as snow levels continue to drop
into D4.


...Northern Plains/Upper Midwest/Western Great Lakes...
Days 1-3...

Anomalously deep closed low developing across the Upper Midwest
and deepening over the Great Lakes is forecast to drop to as low
as -3 standard deviations compared to climatology for 500mb
heights. This low will become a sprawling gyre centered over the
Great Lakes by Friday morning, and the extremely amplified pattern
will drive very slow movement of features through the period.

A surface low beneath this strengthening upper low will move
across MN D1, then WI on D2, and finally fill and eject out of MI
on D3. This low will initially deepen, but as it occludes and
becomes vertically stacked it will remain generally of the same
intensity as it drifts eastward through late week. Despite a lack
of additional forcing, deep warm and moist advection surging out
of the Gulf of Mexico on a LLJ reaching 40+ kts will drive
anomalous moisture into the system, with the WCB driving the
theta-e ridge northward into a TROWAL to support heavy
precipitation. The combination of continued moisture and periodic
vorticity impulses will persist ascent and snowfall across the
Northern Plains/Upper Midwest through the period, with some
enhancement possible as a deformation axis attempts to stretch
somewhere near the MN/ND border Wed into Thu. Additionally,
enhancement in snowfall is likely due to upslope and cooler
thermal profiles in the higher terrain of the Iron Ranges of the
MN Arrowhead, the Coteau des Prairies, Pembina Escarpment, the
Black Hills, and due to LES on the south short of Lake Superior
near the Bayfields Peninsula.

On D1, WPC probabilities for more than 4 inches are high in the MN
Arrowhead where locally more than 12 inches is possible in the
higher terrain due to upslope and lake enhancement. Additional
high probabilities for more than 4 inches exist in the Black Hills
and eastern SD on D1. Late D1 into D2, the deformation axis may
become most intense and spin across western MN leading to a
moderate risk of more than 4 inches of snowfall on D1.5 according
to WPC probabilities. As the low begins to pivot eastward, strong
CAA will cause LES south of Lake Superior from the Bayfields
Peninsula of WI eastward along the U.P. of MI. WPC probabilities
on D2 and D3 exceed 50%, but the total areal coverage of snowfall
should wane each day.


For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.

Weiss

$$




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FOUS11 KWBC 060801
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
400 AM EDT Wed Apr 06 2022

Valid 12Z Wed Apr 06 2022 - 12Z Sat Apr 09 2022

...Pacific Northwest...
Day 3...

Very late Day 2 into Day 3, confluent mid-level flow and warm air
advection will increase moisture into the northeast Pacific
(narrow axis back toward Hawai'i) and eventually into
Washington/Oregon. Precipitable water values will briefly surge to
+1 to +2.5 sigma as a surface cold front moves into the region
beneath modest upper diffluence as the jet streak weakens Friday.
Snow levels will be high to start (6000-7000ft) at precip onset
early Friday but will fall to about 3000ft by the evening.
Progressive flow and modest moisture/upslope will limit amounts
but higher elevations above pass level will still see more than a
foot of snow. With lowering snow levels during the event, some of
the passes will see rain changing to snow and accumulating a few
inches.


...Northern Plains/Upper Midwest/Western Great Lakes...
Days 1-3...

Deep closed low over Minnesota at the start of the period (500mb
heights about -2 to -3 sigma) will wobble eastward through the
period as infused vort maxes from Canada elongate the circulation
into a multi-spoke entity. Though not completely cut off from the
westerlies, it will be a slow-mover (typical for April). On Day 1,
tapped Gulf moisture will surge northward on the WCB (40+ kt 850mb
LLJ) into a TROWAL as the occlusion grows in length across the
Great Lakes, focusing snowfall over southern Ontario and into the
Arrowhead. To the northwest of the low, deformation axis will be a
second focus of modest snowfall over northwestern MN. Third area
will be over the Black Hills as another mid-level vort swings
through with favorable upslope.

By Day 2, the system will overturn as the parent circulation
essentially detaches from the eastern baroclinic zone as the jet
strengthens into the Mid-Atlantic and moisture axis focuses into
southeastern Canada. However, leftover moisture over the Upper
Midwest/Great Lakes will be sufficient for numerous snow showers
with local enhancement especially over the Coteau des Prairies and
Pembina Escarpment. Lake effect/enhanced snow will be favored over
the Gogebic Range into northern WI and the western U.P. as the
flow around the surface low converges across Lake Superior. By Day
3, system will continue to slowly weaken and unwind but the cold
pool aloft will drive plenty of snow showers farther southeast,
reaching through the Midwest and into the southern/central
Appalachians where a couple inches of snow are possible.

WPC probabilities for at least four inches of snow are moderate to
high over the aforementioned favored areas in MN into the Black
Hills Day 1, then into northern WI and the western U.P. of
Michigan Day 2. By Day 3, probabilities decrease over the U.P.
while far northwestern Maine has a low chance of at least four
inches Day 2.5. For the three-day period, low chances of four
inches of snow extends through much of Minnesota into western
ND/SD.


For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.

Fracasso


$$




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FOUS11 KWBC 061957
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
355 PM EDT Wed Apr 06 2022

Valid 00Z Thu Apr 07 2022 - 00Z Sun Apr 10 2022

...Pacific Northwest...
Day 3...

On D3, a shortwave lifting onshore WA state will be on the front
edge of a 130kt Pacific jet streak and accompanied by confluent
flow south of the shortwave to drive ascent and moisture onshore.
This modest AR surging into the Pacific Northwest will surge PWs
to as much as +2 standard deviations above the climo mean, with
IVT slightly above normal as well according to NAEFS ensemble
tables. With the pronounced leading WAA, snow levels will be
generally 6000-7000 ft ahead of the cold front, but drop to around
3000 ft Saturday. While this will keep the heaviest snow above
pass level, where WPC probabilities for 6+ inches are above 80% in
the WA Cascades, as snow levels drop late D3 modest accumulations
of snow are possible at the passes including Snoqualmie and
Stevens after the changeover from rain.


...Northern Plains/Upper Midwest/Western Great Lakes...
Days 1-2...

Anomalous closed low progged to approach -3 standard deviations
compared to climo at 500mb will continue to spin slowly across the
Northern Plains and Upper Midwest into Friday before filling and
opening while ejecting into Canada Saturday. This closed low will
be repeatedly reinforced by spokes of vorticity swinging through
the trough, and interact with at least subtle diffluence within
the LFQ of a downstream intensifying jet streak. These features
together will drive a slow moving surface low pressure from WI
through MI D1 into D2 before weakening into a trough.

Precipitation around this low will be driven by three primary
mechanisms. The first, on D1, will be associated with impressive
WAA on an 850mb LLJ reaching 40 kts emerging from the Gulf of
Mexico. This robust and moist ascent will surge a theta-e ridge
into the region, upon which the deep layer ascent will produce
precipitation, which will fall as snow where the thermals are
supportive. For D1, this is likely in a region near Duluth, MN and
into northern WI and the western U.P. of MI where WPC
probabilities for more than 4 inches are as high as 70% just east
of the Bayfields Peninsula. The second driver of wintry precip,
also on D1, is where the theta-e ridge surges cyclonically into a
TROWAL on the WCB, and interacts with a modest deformation axis NW
of the surface low. The guidance continues to struggle with how
impressive the ascent will be within this deformation, but the
presence of the TROWAL suggests at least enhanced ascent and a
moistening column, so heavy snow is possible D1 within this
region. Where the band sets up, which is most likely from
northeast SD through far northwest MN, WPC probabilities for more
than 4 inches are above 50%, highest in the higher terrain
including the Coteau des Prairies and the Pembina Escarpment.

The final driver of heavy snow will occur on D2 as the low pulls
southeast into MI. As this occurs, robust CAA on northerly winds
will converge over Lake Superior and drive robust LES along the
south shore, including the Porcupine and Huron Mountains, as well
as the Keweenaw Peninsula. The LES should be short lived and wind
down by the end of D2 /Friday evening/, but WPC probabilities for
more than 4 inches are above 80%, and more than 8 inches is
possible in local maxima.


For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.

Weiss


$$




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FOUS11 KWBC 070811
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
409 AM EDT Thu Apr 07 2022

Valid 12Z Thu Apr 07 2022 - 12Z Sun Apr 10 2022

...Pacific Northwest to the Northern Rockies...
Days 2-3...
A mid-to-upper level shortwave trough and its associated surface
cold front are expected to push across the Northwest into the
northern Rockies Friday night into Saturday. In its wake, deep
northwesterly flow with embedded energy aloft will follow,
supporting additional showers through early Sunday. Snow levels
will fall quickly behind the front, dipping below 1000 ft across
portions of the Northwest and the northern Rockies over the
weekend. Two day totals ending Sunday will likely exceed 8 inches
across the Olympics and a large portion of the Washington and
northern Oregon Cascades, including many of the passes. Heavier
amounts are likely for the higher peaks. Locally heavy amounts
are also possible for the Blue Mountains and portions of the
northern Idaho and northwestern Montana ranges.

...Upper Midwest/Western Great Lakes...
Days 1-2...
An anomalously deep closed low will dip southeast from northern
Minnesota into Wisconsin later today. Northerly winds on the
backside of the low will support the development of lake effect
snow showers, focusing initially along the South Shore of Lake
Superior from northern Wisconsin into the western U.P. of
Michigan, where WPC probabilities indicate accumulations of 4
inches or more are likely, and 8 inches or more are possible by
Friday morning. As the low continues to track southeast, backing
winds will spread lake effect snow showers farther east along the
U.P., with locally heavy amounts from the Keweenaw Peninsula into
the central U.P. snowbelt.

For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.

Pereira



$$




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FOUS11 KWBC 071915
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
313 PM EDT Thu Apr 07 2022

Valid 00Z Fri Apr 08 2022 - 00Z Mon Apr 11 2022

...Pacific Northwest to the Northern High Plains...
Days 1-3...

A potent shortwave diving into the Pacific Northwest will be
accompanied by a fast moving jet streak which will push a surface
cold front onshore Friday morning. Ahead of this front, WAA and
confluent mid-level flow combined with the Pacific jet streak will
surge moisture onshore as an AR, with IVT progged to reach 500
kg/m/s on D1. This will spread moisture into the Cascades Friday,
but snow levels are likely to be quite high, above 7000 ft, in the
pre-frontal airmass. However, behind the front, snow levels crash
quickly Friday night, becoming 1000-1500 ft in the Cascades, and
these lowering snow levels will expand eastward into the Rockies
and southward into the Great Basin through the weekend, and may
drop well below 1000 ft Sunday. While the best moisture and ascent
are expected Friday ahead of the trough, persistent mid-level
confluent and zonal flow will maintain moist advection and
favorable ascent into the terrain through all 3 days of the
forecast period.

For D1, WPC probabilities for more than 6 inches are less than 30%
and confined to just the northern WA Cascades due to the high snow
levels. However, by D2 heavy snow becomes more expansive as far
east as the Northern Rockies, with significant accumulations
expanding across the WA Cascades, into the OR Cascades, and in the
Olympic Range. Locally more than 12 inches of snow is likely on D2
in the WA Cascades. Precipitation expands even further on D3 with
snowfall likely as far east as the Wind Rivers and Black Hills as
precipitation continues to surge onshore in waves, but may be more
snow-showery at times, especially inland from the Cascades. WPC
probabilities for more than 6 inches are above 70% across most of
the Cascade Crest of OR and WA, with 30-50% widespread in the
terrain from the Blue Mountains of OR eastward to the Black Hills
of SD.

With snow levels falling quickly D2 and D3, heavy snow is likely
to begin to impact the Cascade Passes, and WPC probabilities are
high for more than 6 inches at many of the passes including
Stevens and Snoqualmie on D2, expanding south towards Santiam Pass
on D3. Travel could become quite difficult due to heavy snow rates
of more than 1"/hr accumulating to several inches at these passes
during the weekend. Additionally, as snow levels drop below 1000
ft, especially Sunday, even some late-season light lowland snow
accumulations are possible.


...Upper Midwest/Western Great Lakes...
Day 1...

The slow moving, anomalously deep, closed upper low will continue
to plague the Upper Midwest, beneath which a surface low will
drift from WI to MI on D1 before exiting into the Northeast D2.
Although the low will be vertically stacked and forcing will be
waning, moisture will remain above normal, especially where
trajectories off the Great Lakes inject moisture into the column.
Strong CAA/north flow behind the departing low will converge over
Lake Superior, and this additional moisture from the lake combined
with upslope flow on the south shore will lead to heavy LES on D1,
especially along the Huron and Porcupine Mountains where WPC
probabilities for more than 4 inches are above 80%. Locally, more
than 8 inches of snowfall is likely in this terrain. Additional
moderate to heavy snow is likely anywhere along the south shore of
Lake Superior from the MN/WI border eastward to the central U.P.
By late D1 into D2, forcing even from LES begins to wane and only
light additional accumulations are expected into D2.

Additionally on D1, steepening lapse rates beneath the upper low
could allow for convectively enhanced snow showers to occur
anywhere from western Iowa through the L.P. of MI. Snowfall rates
may briefly reach 1"/hr as shown by low HREF probabilities, but
accumulations within these showers is expected to be very light.


For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.


Weiss



$$




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FOUS11 KWBC 080757
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
356 AM EDT Fri Apr 08 2022

Valid 12Z Fri Apr 08 2022 - 12Z Mon Apr 11 2022

...Pacific Northwest to the Northern High Plains...
Days 1-3...
A cold front associated with a well-defined mid-to-upper level
shortwave is forecast to move onshore later this morning before
sweeping south and east across the Northwest into the northern
Rockies later today into the overnight, and then into the High
Plains by tomorrow morning. While moisture with the system is
limited, it will mark the onset of significantly colder
temperatures across the region. By late today and continuing
through the overnight, snows levels are expected to drop notably
across the region -- dipping below 1000 ft across much of
Washington, Oregon, northern Idaho, and western Montana by
tomorrow morning. Additional decreases are forecast both Saturday
and Sunday night, with levels dropping below 500 ft across many
areas both nights. While widespread heavy precipitation is not
expected with the front, northwesterly flow its wake with embedded
energy aloft will likely support showers through Sunday before a
developing closed low begins to move onshore Monday morning.
Widespread snow accumulations of 8-12 inches, with heavier amounts
across the higher peaks, are likely for the Olympics, and the
Washington and northern Oregon Cascades. With snow levels
plunging, heavy accumulations are likely for the northern Cascade
passes, with WPC probabilities indicating accumulations of 8
inches or more likely by Sunday morning at both Snoqualmie and
Stevens passes. Locally heavy accumulations are also possible
farther to the east across the higher elevations of the Blue
Mountains and the northern Rockies from northern Idaho and
northwestern Montana to northwestern and north-central Wyoming.

...Western Great Lakes to the Central Appalachians...
Days 1-2...
Northwesterly flow on the backside of a deep closed low that is
slowly drifting east across the western Great Lakes will continue
to support lake effect snow showers, with some additional locally
heavy amounts possible along the western to central U.P. of
Michigan today. Showers are expected to diminish as the low
begins to gradually fill and lift out over the weekend.
Meanwhile, deep cyclonic flow will support snow showers over the
central and southern Appalachians, with light accumulations
possible across the higher elevations today and tomorrow, before a
shortwave ridge begins to shift east across the region on Sunday.

For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.

Pereira



$$




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FOUS11 KWBC 082039
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
438 PM EDT Fri Apr 08 2022

Valid 00Z Sat Apr 09 2022 - 00Z Tue Apr 12 2022

...Pacific Northwest to the Northern High Plains...
Days 1-3...

A cold front sweeping south and east across the Northwest marks
the onset of a return to wintry conditions across The West that
continues through the middle of next week. Snow levels are
dropping across the region, reaching 1000 ft across much of
Washington, Oregon, northern Idaho, and western Montana by late
tonight. These snow levels are maintained as cold air spreads
across the rest of the Northwest Saturday. Reinforcing troughing
brings the coldest air to the PacNW coast Saturday night with snow
levels there dropping to 500 ft into Sunday.

The combination of reinforcing waves likely results in a closed
low over WA or OR by Sunday night. The GFS and UKMET have been
bullish with this low and thus a faster/more northern solution
than the more open/positively tilted trough off the PacNW that is
slower in the EC/CMC. 12Z guidance still has a disconnect between
these two camps, though the EC/CMC did shift north with their QPF
solutions with the CMC (and perhaps more specifically the
CMC_regional) being the best compromise at this time for precip.
We will see if this trend toward a compromised solution between
these camps continues. Overall, a northern trend in the main
precip axis both over the Northwest Sunday night into Monday and
toward the northern High Plains Monday into Monday night is noted.
There is still the risk for a powerful winter storm to develop
early next week with strong winds and banded heavy snow.

Days 1-3 there is confidence in the heavy snow threat shifting
south from WA on Day 1 (high probs for over 6" in the Cascades),
into OR Day 2 (high probs for over 6" spread down to the central
OR Cascades) and along the OR Cascades for Day 3 with some
probabilities for over 6" into the northern Sierra Nevada. 2 to 3
feet is likely to fall along the entirety of the WA/OR Cascades
through the next 72hrs. With anomalously low snow levels, heavy
accumulations are likely for the northern Cascade passes, with WPC probabilities indicating accumulations of 8 inches or more likely
by Sunday morning at both Snoqualmie and Stevens passes. Locally
heavy accumulations are likely with a leading reinforcing impulse
coming off the building through in the PacNW on Day 2 across the
higher elevations of the Blue Mountains and the northern Rockies
from northern Idaho and northwestern Montana to northwestern and
north-central Wyoming and the Black Hills.


...Great Lakes to the Central Appalachians...
Days 1-2...

Northwesterly flow continues on the backside of a deep
closed/occluded low that is drifting across eastern Ontario this
afternoon will continue to support locally moderate lake effect
snow showers over the U.P. into this evening. Meanwhile, deep
cyclonic flow will support moderate to locally heavy snow showers
over the central and southern Appalachians tonight through
Saturday night. Day 1 snow probabilities for over 4" are
moderately high for the Allegheny Highlands of east-central WV and
for the Great Smokies.
Ridging the wake of this anomalously deep low begins to shift east
across the region on Sunday, cutting off the upslope flow.


For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.

Jackson



$$




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FOUS11 KWBC 090847
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
445 AM EDT Sat Apr 09 2022

Valid 12Z Sat Apr 09 2022 - 12Z Tue Apr 12 2022

...Pacific Northwest to the Northern High Plains...
Days 1-3...
A strong cold front continues to push southeast across the
northwestern corner of the CONUS this morning. In its wake, deep
northwesterly flow with embedded energy aloft will support showery
and unseasonably cold weather today across the Northwest into the
northern Rockies. Already low snow levels are expected to dip
further tonight, dropping below 500ft across much of Washington,
eastern Oregon, and the northern Rockies by tomorrow morning.
Models show a fairly well-defined shortwave moving onshore,
supporting some organized precipitation along the coast from
Washington to the North Coast of California tomorrow morning.
However, a greater chance for heavier precipitation is expected to
develop tomorrow night and continue into Monday as a closed low
forms offshore and moves inland. As the low moves across the
region Monday and Tuesday, the GFS shows 500mb heights dropping
2-3 standard deviations below normal across the Northwest into the
northern Rockies. With snow levels remaining low, minor
accumulations are possible across the lowlands and interior
valleys of Washington and Oregon. Several inches are possible in
the higher elevations of coastal ranges, with heavy amounts of a
foot or more likely for the southern Washington and Oregon
Cascades. A shortwave digging south of the low will support snow
spreading south from the Northwest California mountains into the
Sierra on Monday, with heavy amounts possible across the higher
peaks.

As the low continues to move east, accumulating snows are likely
to reach down to the valley floors of eastern Washington, Oregon,
and Idaho, with heavy accumulations possible for the northeastern
Oregon and central Idaho ranges. Snow is expected to develop east
of the Divide across the northern High Plains Monday night into
early Tuesday. Increasing upslope flow on the northwest side of a
low moving east of the Rockies, along with divergence aloft near a
coupled jet, will support heavy snows developing over the central
to western Montana ranges Monday night into Tuesday.

...Upper Midwest...
Day 2...
A shortwave dropping into the Northwest later today is forecast to
move across the northern Plains tomorrow and then lift north,
assuming a negative tilt as it tracks across the Upper Midwest
Sunday night and Monday morning. This dynamic system is expected
to support rain changing to snow across northern Minnesota late
Sunday into early Monday. With the GFS continuing to back away
from its more amplified solution, it is now in better agreement
with the general model consensus of an inch or two or likely, but
with some potential for heavier amounts given the dynamics of the
system.


For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.

Pereira


$$




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FOUS11 KWBC 092043
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
443 PM EDT Sat Apr 09 2022

Valid 00Z Sun Apr 10 2022 - 00Z Wed Apr 13 2022

...Western U.S. to the Northern Rockies...
Days 1-3...
Anomalous cold from deep northwesterly flow expands across the
Northwest through the northern High Plains through Sunday under
reinforcing upper troughing. Through Sunday, embedded energy aloft
will support showery and unseasonably cold weather across the
Northwest and the northern Rockies. Already low snow levels will
dip further tonight, dropping below 500ft across much of
Washington, eastern Oregon, and the northern Rockies by Sunday
morning where Day 1 probabilities for over 4" snow are generally
moderate (high for the WA to central OR Cascades where there are
moderate probabilities for over 12").

12Z guidance is in better agreement for a shortwave trough axis
currently near the AK Panhandle amplifying as it shifts south off
the BC through Sunday before closing into an upper low over
western WA/OR Sunday night. Upper forcing from this developing low
(including left jet exit lift) along with ample Pacific moisture
rounding the wave will make for particularly heavy precipitation
along with low snow levels, a rare pairing for the Northwest
(particularly for April) with a focus on western OR Sunday night
and northern CA Monday. Snow levels in the heavier precip look to
be around 3000ft, lowering back down to 2000ft after the trough
passage. Day 2 snow probabilities are moderate for over 8" from
the southern WA Cascades through the northern Sierra and high for
the OR Cascades (where there are moderate probabilities for over
18").

The low opens into a wave again (with a neutral tilt) and shifts
inland over the northern Great Basin late Monday, reaching the
northern Rockies Tuesday. A focused wave of precip shifts east
ahead of this trough axis with snow levels over the northern Great
Basin generally 4000 to 5000ft in the warm air advection through
Monday evening. Late Monday night, the heavy snow focus shifts to
the lee-side as rapid surface cyclogenesis occurs over
northeastern CO. Day 2.5 snow probabilities are moderate for 8 or
more inches across north-central OR terrain (including the Blue
Mtns in Northeast OR), central ID terrain into southeast MT, as
well as the Wasatch of northern UT.

...Northern Rockies to northern Great Plains...
Day 3...
The aforementioned lee-side cyclogenesis over northeast CO Monday
night combined with a 1040mb surface high over northern Alberta
sets up intense low level convergence with an upslope component
from very strong northeasterly flow over the northern High Plains
and eastern slopes of the northern Rockies late Monday night
through Tuesday before shifting farther east on the northern
Plains Tuesday night. The focus of the convergent axis of precip
has shifted over the past few days, with the latest trend to focus
a bit farther south over central/eastern MT to near the ND/SD
border. 12Z deterministic consensus is in good agreement with each
other. The 12Z ECMWF is a bit farther south than the rest of the
consensus, but the threat for a blizzard remains strong. Day 3
probabilities for over 12" are moderate across south-central MT
with moderately high probabilities for over 8" from the eastern
slopes of the MT Rockies (south of Glacier NP) east to the Dakota
border.

Further reinforcement of the trough over the northern High Plains
from the Pacific Northwest Tuesday night leads to a negative tilt
and pivot of the surface low track that likely brings it up the
eastern side of the northern Plains, maintaining a threat for
windy/heavy snow over the Dakotas through Wednesday.


...Northern Minnesota...
Days 1/2...
A shortwave trough crossing the northern Rockies this evening is a
reinforcing trough of a notable cold outbreak that overspreads the western/northern CONUS through the middle of next week. This
trough axis assumes a negative tilt as it tracks from the Dakotas
and across Minnesota Sunday night. This dynamic system is expected
to support rain changing to snow in embedded bands over
northwestern Minnesota Sunday evening, expanding over the
Arrowhead late Sunday night. The risk for briefly heavy snow is
next over north-central MN where Day 1.5 snow probabilities for
over 4" are around 20%.


For Days 1-3, the probability of at least 0.1" icing is less than
10 percent.

Jackson


$$




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FOUS11 KWBC 100905
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
503 AM EDT Sun Apr 10 2022

Valid 12Z Sun Apr 10 2022 - 12Z Wed Apr 13 2022

...Western U.S. to the Northern Plains...
Days 1-3...
A late season, long duration winter storm, producing significant
snow and strong winds will likely impact the northwestern to the
north-central U.S. this period.

Unsettled weather will continue across the Northwest today as an
upper level shortwave and its associated frontal band continue to
move across the region this morning. This will be followed by a
more amplified system moving into the region later today. Models
show a closed low developing just east of Vancouver Island later
today before pivoting southeast into Washington and Oregon
tomorrow. This will bring another round of heavier precipitation
and strong winds, followed by lower snow levels behind a strong
cold front moving across Oregon and northern California on Monday.
In addition to heavy snows for the southern Washington and Oregon
Cascades, significant accumulations are possible along the higher
elevations of the coastal ranges as well. Energy digging south of
the low will draw colder air and onshore flow farther south across
Northern California, supporting mountain snows with potentially
heavy accumulations spreading south from the Northwest California
ranges into the Sierra on Monday.

As this system moves east, accumulating snows are likely to reach
down into the valleys of southeastern Washington, eastern Oregon,
and Idaho, with heavy accumulations possible for the Blue
Mountains into the northern and central Rockies from central Idaho
and western Montana to Utah on Monday into early Tuesday. Snow is
expected to develop east of the Divide across the northern High
Plains Monday night into early Tuesday. Increasing upslope flow
on the northwest side of a low moving east of the Rockies, along
with divergence aloft near a coupled jet, will support heavy snows
developing over the central to western Montana ranges Monday night
into Tuesday. Meanwhile, persistent onshore flow ahead of another
system developing along the British Columbia coast will support
continued unsettled weather across western Washington and Oregon,
into Northwest California, with additional heavy accumulations
possible along the Cascades and coastal ranges.

On Tuesday heavy snow is likely to develop and spread east from
central Montana into parts of the Dakotas. As the leading low
continues to track east, strong low-to-mid level frontogenesis on
the northwest side of a powerful, deepening surface low that is
expected to track northeast from the central High Plains to the
Upper Midwest, overlapped by coupled upper jet forcing, will
support heavy snow developing across the region. Model spread
remains significant, with the GFS and GEFS Mean still faster than
the ECMWF, UKMET, and CMC to bring the low east into the northern
Plains Wednesday morning. While the spread does lower confidence
in the details, heavy snowfall accumulations and strong winds will
likely impact a significant portion of southeastern Montana,
northwestern South Dakota and southwestern to central North Dakota
by early Wednesday. WPC probabilities indicate that by Wednesday
morning widespread snowfall accumulations of 8-12 inches, with
locally heavier amounts are likely across the region.

...Northern Minnesota...
Days 1...
A shortwave moving east of the northern Rockies this morning is
forecast to track across the northern Plains today and then lift
north, assuming a negative tilt as it tracks across the Upper
Midwest tonight into Monday morning. This dynamic system is
expected to support rain changing to snow across northern
Minnesota later today into early Monday. Model consensus
continues to show that an inch or two of snow is likely, with some
potential for heavier amounts given the strong dynamics.

For Days 1-3, the probability of at least 0.1" icing is less than
10 percent.

~~~Key Messages for April 11-14 Winter Storm~~~

--A late season, long duration, significant winter storm is likely
to affect portions of the northern Rockies, northern Plains, and
Upper Midwest Monday into Tuesday.

--While uncertainty remains regarding the details of the track and
timing of this system, heavy snow and strong winds are possible
for many areas.

--The combination of heavy snow rates and strong winds could
produce blizzard and near-blizzard conditions, creating hazardous
travel.

--Heavy wet snow producing significant accumulations has the
potential to produce scattered power outages, tree damage, and may
impact livestock, especially young calves and lambs.

--Begin to prepare for impactful winter weather and hazardous
travel conditions this week.

Pereira


$$




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