• MESO: Mesoscale Discussion 1170

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Wed Jul 7 00:41:04 2021
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    ACUS11 KWNS 070041
    SWOMCD
    SPC MCD 070040=20
    MTZ000-070215-

    Mesoscale Discussion 1170
    NWS Storm Prediction Center Norman OK
    0740 PM CDT Tue Jul 06 2021

    Areas affected...Parts of central/eastern Montana

    Concerning...Severe Thunderstorm Watch 339...

    Valid 070040Z - 070215Z

    The severe weather threat for Severe Thunderstorm Watch 339
    continues.

    SUMMARY...Widely scattered strong storms may pose a continuing risk
    for severe hail and locally strong surface gusts through mid to late
    evening. While there appears some potential for the evolution of a
    small upscale growing cluster, particularly near/east of Havre into
    areas northeast of Lewistown, this threat still appears relatively
    low and it is not yet clear that another severe weather watch is
    needed.

    DISCUSSION...Easterly to southeasterly near surface flow, to the
    cool side of a zone of stronger differential surface heating and
    deeper boundary-layer mixing to the east of the higher terrain, has
    maintained sufficient boundary-layer moisture to contribute to CAPE
    on the order of 1000-1500 J/kg. This is not particularly large, but
    even within this regime, the boundary-layer is still relatively
    deeply mixed. And perhaps more prominently, beneath a belt of 40+
    kt northwesterly flow around 500 mb, deep-layer shear is strong.

    The environment has become conducive to widely scattered supercell
    development as far north as southern Alberta and Saskatchewan,
    perhaps aided by weak warm advection around the 700 mb level. It is
    possible that this forcing could contribute to some continuing
    upscale growth of ongoing convection into the 03-06Z time frame.=20
    However, synoptic forcing for ascent appears otherwise weak, and it
    might be just as possible that much of ongoing activity could begin
    to wane as boundary-layer cooling progresses, given the already
    somewhat marginal nature of the thermodynamic profiles.

    ..Kerr.. 07/07/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!v0PlrY8ZTNBfdM0hRr7NF_q_5fMVeBGH52tP8f8z35MDqNEiTYnksdSEYZ38zuOUsnpBVSQl$=
    for graphic product...

    ATTN...WFO...BYZ...GGW...TFX...

    LAT...LON 48770857 47020557 45590716 45930854 47731007 48841125
    48770857=20



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