• MESO: Mesoscale Discussion 1358

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Monday, July 04, 2022 19:29:48
    ACUS11 KWNS 041929
    SWOMCD
    SPC MCD 041929=20
    MTZ000-042230-

    Mesoscale Discussion 1358
    NWS Storm Prediction Center Norman OK
    0229 PM CDT Mon Jul 04 2022

    Areas affected...Parts of southwestern through central Montana

    Concerning...Severe potential...Watch possible=20

    Valid 041929Z - 042230Z

    Probability of Watch Issuance...60 percent

    SUMMARY...A corridor of intensifying organized thunderstorm
    development, including sustained supercells, may evolve south of
    Helena into the Lewistown vicinity through 4-6 PM MDT. Trends are
    being monitored, and it is possible that a severe weather watch may
    eventually be needed.

    DISCUSSION...Downstream of a mid-level low and associated troughing
    slowly progressing inland of the Pacific Northwest coast,
    large-scale ascent coupled with weak to modest boundary-layer
    destabilization likely will contribute to increasing scattered
    thunderstorm development across the mountains of western through
    south central Montana during the next few hours.

    Models indicate a corridor of strengthening lower/mid tropospheric frontogenetic forcing and warm advection south of Helena toward the
    Lewistown vicinity through 22-00Z. This may provide the focus for
    the more sustained and vigorous thunderstorm activity, coincident
    with the strongest deep-layer mean shear (40-50 kt) and ambient west-southwesterly mean flow (around 30 kt). With another several
    hours of daytime heating, mixed-layer CAPE may increase in excess of
    1000 J/kg, gradually contributing to an environment increasingly
    conducive to evolution of isolated supercells with the potential to
    produce severe hail and locally strong surface gusts.

    ..Kerr/Grams.. 07/04/2022

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!_hfU7imRWQ9SL_4R8C7J-rM0dMm4V0VoGQ4s2aYUAdZUKYIKcSC23dr7RgDMMZ9NjdCOgOQ5d= pLdKMP4CW2sRcS5HSg$ for graphic product...

    ATTN...WFO...BYZ...TFX...MSO...

    LAT...LON 47101113 47240924 46350951 45731184 46331279 47101113=20


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  • From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Friday, June 30, 2023 19:33:20
    ACUS11 KWNS 301933
    SWOMCD
    SPC MCD 301932=20
    KYZ000-INZ000-TNZ000-ILZ000-MOZ000-302200-

    Mesoscale Discussion 1358
    NWS Storm Prediction Center Norman OK
    0232 PM CDT Fri Jun 30 2023

    Areas affected...east-central Missouri...west-central and southern Illinois...far southwest Indiana and western Kentucky

    Concerning...Severe potential...Severe Thunderstorm Watch likely=20

    Valid 301932Z - 302200Z

    Probability of Watch Issuance...80 percent

    SUMMARY...Thunderstorm clusters capable of severe, damaging gusts,
    and large to very large hail are expected by 23z. A severe
    thunderstorm watch is likely in the next couple of hours.

    DISCUSSION...An expansive cumulus field is noted to the south of an
    outflow boundary across southeast MO into southern IL and western
    KY/far southwest IN. Surface dewpoints across the region generally
    range from 75-79 F amid 90s F temperatures. This is aiding in strong instability, with MLCAPE values from 2500-4500 J/kg. This
    environment has allowed for deepening of the cumulus field over the
    past hour or so, with some towering cumulus now evident in visible
    across east-central MO just south of the I-70 corridor. Convective
    initiation is expected by 22-23z. Initial cells are expected to
    quickly cluster and propagate toward the east/southeast near the
    instability gradient. This activity is expected to remain on the
    southern edge of a zone of stronger effective shear, but shear will
    be sufficient for storm organization. Very steep low-level lapse
    rates, coupled with strong instability, will support intense
    downdrafts. Thunderstorm clusters will be capable of severe gusts, a
    few greater than 65 kt. While clusters are expected, the more
    intense and/or discrete cores will be capable of large hail. Steep
    midlevel lapse rates and somewhat elongated hodographs (per regional
    forecast soundings) in the presence of large instability between
    700-300 mb suggest isolated very large hail (greater than 2.5 inch
    diameter) is possible. While some uncertainty in timing of
    convective initiation exists due to a lack of stronger large-scale
    ascent, a severe thunderstorm watch will likely be needed by around
    21-22z.

    ..Leitman/Grams.. 06/30/2023

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!82iKTFRp0FvmF0c4l4o92-zTJzdtLqfFtRjrXyPBS3XiCpePT1TRNNushunoTCS87-otf7www= ooBxMcDXr6jIANQhSQ$ for graphic product...

    ATTN...WFO...OHX...PAH...ILX...LSX...

    LAT...LON 36628791 36618849 36938947 37229011 37729099 38219143
    38329149 38649152 38879142 39069095 39138992 38998909
    38278742 37448720 37228721 36768747 36628791=20


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