• MESO: Mesoscale Discussion 0789

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Fri May 28 21:55:52 2021
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    ACUS11 KWNS 282155
    SWOMCD
    SPC MCD 282155=20
    MTZ000-WYZ000-290000-

    Mesoscale Discussion 0789
    NWS Storm Prediction Center Norman OK
    0455 PM CDT Fri May 28 2021

    Areas affected...portions of southeast Montana into extreme northern
    Wyoming

    Concerning...Severe potential...Watch unlikely=20

    Valid 282155Z - 290000Z

    Probability of Watch Issuance...20 percent

    SUMMARY...Large hail and gusty winds may accompany the stronger
    storms into the early evening hours. A WW issuance is unlikely given
    the expected sparse coverage of severe wind/hail.

    DISCUSSION...Multicellular thunderstorm clusters have been gradually
    increasing in coverage and intensity across Yellowstone Country over
    the past couple of hours given increased deep-layer ascent by a
    passing mid-level trough. These storms are developing atop a dry
    boundary layer, with the latest METAR observations showing up to 30F temperature/dewpoint spreads, and RAP forecast soundings indicating
    a dry sub-cloud layer extending up to 500 mb. Despite the dry
    boundary layer, 8.5-9.5 C/km low and mid-level lapse rates are
    promoting up to 1000 J/kg SBCAPE, with some convective
    organization/sustenance possible given 35+ kts of effective bulk
    shear.=20

    Much of the CAPE is contained above 700 mb, and is characterized by
    low CAPE density. As such, large hail may accompany the more robust,
    longer lasting multicellular clusters. Damaging gusts are also
    possible given efficient evaporative cooling and downward momentum
    transport within the steep lapse rate/dry low-level environment.
    Nonetheless, overall convective coverage and associated brief severe
    threat is expected to be relatively isolated overall, and a WW
    issuance is not expected.

    ..Squitieri/Edwards.. 05/28/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!uIzwgvDM1X6Hry4J7HdPEsj9fSf3c9Ti-nk2ChMjQe-asxYu58uVpIV01xIpPJhlSvArn9xY$=
    for graphic product...

    ATTN...WFO...UNR...BYZ...RIW...

    LAT...LON 45950950 46340762 46490643 46500498 46460453 46000409
    45620414 45090428 44740467 44590564 44640684 44820766
    45000887 45390944 45950950=20



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