• MESO: Mesoscale Discussion 1299

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Fri Jul 16 20:17:13 2021
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    ACUS11 KWNS 162017
    SPC MCD 162016=20

    Mesoscale Discussion 1299
    NWS Storm Prediction Center Norman OK
    0316 PM CDT Fri Jul 16 2021

    Areas affected...Southwestern South Dakota and Western Nebraska

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

    Valid 162016Z - 162215Z

    Probability of Watch Issuance...40 percent

    SUMMARY...Storms are expected to increase in coverage and intensity
    across southwestern South Dakota and the Nebraska Panhandle over the
    next couple of hours. Uncertainty remains regarding storm coverage
    and evolution, but convective trends will be monitored for the
    possibility of a severe thunderstorm watch.

    DISCUSSION...Despite midlevel heights rising across the region,
    thunderstorms have initiated over the Black Hills in a moist,
    upslope low-level flow regime. With midlevel lapse rates over 8 C/km
    and surface dewpoints in the low 60s F, MLCAPE values are over 1000
    J/kg with continued destabilization expected through the afternoon.=20
    While westerly midlevel flow is relatively weak (~25 knots per the
    latest UDX VWP), when coupled with easterly-to-southeasterly
    low-level flow, effective bulk shear is around 30-35 knots, which
    should be sufficient for organized storm modes.=20=20

    Current thinking is that a storm or two may move southeastward off
    of the Black Hills with isolated storm development also possible
    southward along the lee trough/dryline. Storms will initially pose a
    threat for severe hail while remaining discrete, then transition to
    a severe wind threat as outflows merge and grow upscale into southeastward-moving clusters. The increasing south-southeasterly
    low-level jet after ~02Z should further promote storm organization
    and/or new storm development, allowing the severe-weather threat to
    persist after dark.

    ..Jirak/Dial.. 07/16/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!owrcf_TFuGYfiUAJQUlH0ZMPCilRr8FvUv4UhDIrCf-5w5YEcIhAe-MXWv2eUoyHEKCqNSxv$=
    for graphic product...


    LAT...LON 44060399 44330371 44200248 43630175 42660129 41750111
    41300185 41270295 42090384 42580405 44060399=20

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