• MESO: Mesoscale Discussion 1326

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Thu Jul 22 19:50:55 2021
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    ACUS11 KWNS 221950
    SWOMCD
    SPC MCD 221950=20
    MTZ000-222215-

    Mesoscale Discussion 1326
    NWS Storm Prediction Center Norman OK
    0250 PM CDT Thu Jul 22 2021

    Areas affected...Much of central Montana

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

    Valid 221950Z - 222215Z

    Probability of Watch Issuance...40 percent

    SUMMARY...Thunderstorms are expected to gradually increase and
    intensify across southwestern into central Montana through 3-6 PM
    MDT, accompanied by at least some risk for severe hail and wind.=20
    More substantive strengthening and organization, accompanied by
    increasing potential for strong surface gusts, may not occur until
    after 6 PM MDT, generally northeast of the Lewistown area.

    DISCUSSION...Forcing for ascent, associated with a weak perturbation
    migrating around the periphery of mid-level ridging centered over
    the Four Corners, appears to be aiding deepening convective
    development and the initiation of thunderstorms across the mountains
    of southwestern into central Montana. This is occurring near the
    southern fringe of stronger flow associated with the westerlies,
    which includes west-southwesterly winds around 500 mb on the order
    of 40-50 kt.

    Lower/mid-tropospheric lapse rates across this region continue to
    steepen in response to insolation and perhaps weak mid-level
    cooling, and moisture appears sufficient to support weak to modest
    CAPE on the order of 500-1000 J/kg. This should be enough to
    support a gradual further increase in convective coverage and
    intensity through the next few hours, with at least some potential
    for stronger storms to pose a risk for hail and locally strong
    surface gusts.

    In time, a more substantive risk for organized severe weather may
    gradually develop, as consolidating convectively driven cold pools
    contribute to the evolution of an organizing convective system in
    the presence of the strong deep-layer shear. This seems most
    probable as activity spreads northeast of the Lewistown area by or
    shortly after 00Z, with severe weather potential increasingly more
    rapidly thereafter, as strong northeasterly low-level inflow
    increasingly emanates from a hotter and more moist environment
    across northeastern Montana.

    ..Kerr/Hart.. 07/22/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!ti1PRgkCJCXxG1eGoL6j4JWjb1AiDcLTqjVGtfkC4wpEOgUhWtmEu7ZKiny5W-YE2SfBoB42$=
    for graphic product...

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

    LAT...LON 46741198 48450859 48130723 46850687 45461098 46741198=20



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