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ACUS48 KWNS 080901
SWOD48
SPC AC 080900
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Fri Apr 08 2022
Valid 111200Z - 161200Z
...DISCUSSION...
A multi-day severe weather event appears likely across parts of the
central CONUS from Day 4/Monday through Day 6/Wednesday. Large hail,
damaging winds, and tornadoes all appear possible each day.
...Day 4/Monday: Southern Plains into the Ozarks...
An upper trough should amplify over the western CONUS on Day
4/Monday. There is still some uncertainty regarding the amplitude
and placement of a leading shortwave trough over the Upper Midwest
vicinity Monday morning. Some convection aided by strong low-level
warm advection may also be ongoing Monday morning over parts of MO.
This activity could impact the northward extent of low-level
moisture return across the southern Plains and Ozarks through the
day. Even with these lingering uncertainties, at least isolated
severe thunderstorms should develop by Monday afternoon along and
east of a surface dryline which should extend across central OK/TX,
as modest ascent preceding the upper trough overspreads the warm
sector. Moderate to strong instability and steep mid-level lapse
rates combined with adequate deep-layer shear suggest a threat for
large hail with any supercells that can develop. Damaging winds may
also occur. Given the gradually increasing low-level moisture and
strengthening low-level jet Monday evening, some threat for
tornadoes should also exist as convection spreads eastward.
...Day 5/Tuesday: Southern/Central Plains into the Mid Mississippi
Valley...
The large-scale upper trough centered over the western states on Day
5/Tuesday is forecast to amplify as it ejects eastward across the
Rockies and adjacent High Plains through Tuesday night. There are
still some large differences between various deterministic models
regarding the placement and amplitude of this ejecting upper trough.
The slower, more amplified solution suggested by the ECMWF and its
ensemble mean would suggest the primary surface lee cyclone may
focus across the central High Plains through Tuesday evening, with a
dryline extending southward across the southern Plains. The faster
and more northern placement of the upper trough by the GFS would
argue for a more northward warm sector development and farther east
surface low placement across the central Plains into mid MO Valley.
Regardless of these differences, severe thunderstorms will likely
develop by Tuesday afternoon along much of the length of the dryline
across the southern/central Plains. The presence of steep lapse
rates aloft, diurnal heating of a moist low-level airmass, and
gradually strengthening deep-layer shear should support a mix of
multicells and supercells capable of producing large hail, damaging
winds, and tornadoes through Tuesday evening.
...Day 6/Wednesday: Southern/Central Plains into the Lower/Mid
Mississippi Valley...
Large differences exist in model guidance by Day 6/Wednesday with
the placement of the upper trough/low ejecting across the Plains.
The slower, more southern solution offered by the ECMWF and its
ensemble mean suggest a substantial severe threat exists along/east
of the dryline from KS/OK/TX extending eastward into parts of the
lower/mid MS Valley. Strong deep-layer shear combined with moderate
to strong instability would support supercells with all severe
hazards possible, including tornadoes. The faster, more northern
solution indicated by the GFS would shift the greatest severe threat
a bit farther east across the lower/mid MS Valley through the day.
The solution offered by the ECMWF has been favored with this
outlook, as it has had run-to-run consistency and strong ensemble
support. Have therefore expanded the 15% severe area to include more
of the central Plains and lower/mid MS Valley. If model agreement
increases, then greater severe probabilities will likely need to be
introduced. An organized severe threat, including the potential for
tornadoes, may continue Wednesday evening/night across the lower MS
Valley and Mid-South regions as a southerly low-level jet
strengthens, enhancing low-level shear in the presence of sufficient boundary-layer instability to support surface-based thunderstorms.
...Day 7/Thursday: Southeast...
Depending on the evolution of the upper trough over the central
CONUS, some severe threat may persist on Day 7/Thursday across parts
of the Southeast. It is possible that convection may already be
ongoing Thursday morning across portions of the lower MS Valley. If
rich low-level moisture can return northward ahead of this activity,
then weak instability coupled with favorable low-level and
deep-layer shear may support a continued threat for organized severe thunderstorms through Thursday evening. At this time, the best
chance for this appears to be over portions of the central Gulf
Coast states. However, given the considerable uncertainty regarding
the evolution/placement of the upper trough at this extended time
frame, and the potential for convection to outpace the low-level
moisture return, a 15% severe area does not appear warranted at this
time.
..Gleason.. 04/08/2022
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