• MESO: Mesoscale Discussion 1739

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Mon Sep 13 23:07:29 2021
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    ACUS11 KWNS 132307
    SPC MCD 132307=20

    Mesoscale Discussion 1739
    NWS Storm Prediction Center Norman OK
    0607 PM CDT Mon Sep 13 2021

    Areas affected...Parts of central and eastern Pennsylvania

    Concerning...Severe Thunderstorm Watch 496...

    Valid 132307Z - 140100Z

    The severe weather threat for Severe Thunderstorm Watch 496

    SUMMARY...The risk for damaging wind gusts may gradually increase
    with an evolving and organizing cluster of storms near the
    Williamsport vicinity into areas between Wilkes-Barre and Allentown
    by 9-10 PM EDT. It is possible a new severe weather watch may
    become needed east of WW 496.

    DISCUSSION...Thunderstorm development continues to increase aided by
    low-level confluence along a weak frontal zone. Forcing for ascent accompanying a remnant MCV and associated mid-level speed maximum
    emerging from the lower Great Lakes region is also probably
    contributing to development, and the environment appears favorable
    for upscale growth and the evolution of an organizing convective

    A moist boundary layer along the southeastern slopes of the
    Allegheny Front appears characterized by sizable CAPE up to around
    2000 J/kg, beneath steep lower/mid tropospheric lapse rates on the
    northern periphery of a remnant plume of elevated mixed-layer air.=20 Deep-layer shear is strong beneath a belt of 40-50 kt
    west-northwesterly flow around 500 mb.

    Although large hail and localized strong gusts currently appear the
    most prominent severe hazards in isolated stronger cells, as
    activity grows upscale, heavy precipitation loading may gradually
    contribute to the downward transport of momentum on a broader scale,
    with increasing risk for damaging surface gusts. The best potential
    for this appears to be with an ongoing clustering of intensifying
    convection currently still north of Williamsport, as it develops east-southeastward into areas west through north of the Allentown
    vicinity by 01-02Z.

    ..Kerr.. 09/13/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!s6Fq0gwQE_8GyBsC1L1zQspGiAD6Vl-w2gVqZTMCC-vdAPuX5sYiwNDbaNDsU6Tm_UoeN1Yq$=
    for graphic product...


    LAT...LON 41217782 41287735 41327672 41227615 41217550 40817563
    40597669 40677743 40867838 41197927 41217782=20

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