• MESO: Mesoscale Discussion 1309

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Sat Jul 17 20:41:22 2021
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    ACUS11 KWNS 172041
    SPC MCD 172040=20

    Mesoscale Discussion 1309
    NWS Storm Prediction Center Norman OK
    0340 PM CDT Sat Jul 17 2021

    Areas affected...Western South Dakota...Nebraska Panhandle...and
    Northeastern Colorado

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

    Valid 172040Z - 172315Z

    Probability of Watch Issuance...40 percent

    SUMMARY...Storms developing over the high terrain are expected to
    eventually move eastward into the High Plains, posing a risk for
    severe hail and wind. The coverage of severe storms remains
    uncertain, so convective trends will be monitored for the
    possibility of a severe thunderstorm watch.

    DISCUSSION...Even though midlevel heights are rising across the
    area, an impulse rounding the top of the ridge has contributed to
    thunderstorm initiation over the high terrain of central
    Colorado/Wyoming and Black Hills of South Dakota. Substantial
    convective inhibition remains over the plains, as indicated by the
    20Z UNR sounding (170 J/kg of MLCIN), which will likely delay the
    threat and limit the eastward extent. Nevertheless, strong heating
    will continue to remove the convective inhibition through the
    afternoon, yielding ~1000 J/kg of MLCAPE with 30-40 knots of
    effective bulk shear by late afternoon/evening (per latest RAP).=20
    This environment should support organized storm modes that pose a
    threat for severe hail initially (midlevel lapse rates around 8
    C/km), followed by a transition to a wind threat as storms merge
    into one or more southward-moving clusters, perhaps aided by a
    southeasterly low-level jet after 02Z. Significant uncertainty
    remains regarding storm coverage, longevity, and evolution, so
    convective trends will be monitored for the possibility of a watch.

    ..Jirak/Dial.. 07/17/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!oMefUg-t5dHgYCXYd2KiLdPDmhr9mwJm17ppllZ42i_Fa_yfdZ6PsQOp63uj2tjmhCz0MEeq$=
    for graphic product...


    LAT...LON 40000377 41000413 42510419 43440414 44100404 44300386
    44280333 44180286 43910261 43570235 43140226 42370220
    41650215 41130210 40650207 40000207 39730276 40000377=20

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