• MESO: Mesoscale Discussion 1323

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Wed Jul 21 14:33:17 2021
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    ACUS11 KWNS 211433
    SPC MCD 211432=20 MAZ000-RIZ000-CTZ000-NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-21153=

    Mesoscale Discussion 1323
    NWS Storm Prediction Center Norman OK
    0932 AM CDT Wed Jul 21 2021

    Areas affected...Parts of northern Virginia...the District of Columbia...central/eastern Maryland...Delaware...southeastern Pennsylvania...New Jersey...southeastern New York including Long Island...Connecticut...Rhode Island and southeastern Massachusetts

    Concerning...Severe potential...Watch likely=20

    Valid 211432Z - 211530Z

    Probability of Watch Issuance...80 percent

    SUMMARY...Scattered intensifying thunderstorm development is
    possible through Noon-2 PM EDT, posing a risk for at least
    marginally severe hail and locally strong surface gusts. With
    storms likely to become more widespread thereafter, a severe weather
    watch probably will be issued.

    DISCUSSION...A slowly southward advancing surface cold front has
    reached southeastern New England and the northern Mid Atlantic
    coast, with large-scale ascent likely to increase in a corridor
    along and ahead of it through early afternoon. This appears likely
    to be aided by forcing ahead of substantive mid-level short wave
    trough gradually turning east of the lower Great Lakes region.

    The strengthening lift will coincide with a narrow pre-frontal
    corridor of rapidly steepening near-surface lapse rates aided by
    daytime heating. Lower/mid tropospheric lapse rates are also
    relatively steep and, despite seasonably modest low-level moisture,
    it appears that this will contribute to mixed-layer CAPE in excess
    of 1000 J/kg (up to around 2000 J/kg).

    Although low-level wind fields are generally weak, 30-50+ kt
    cyclonic flow in the 500-300 mb layer is contributing to sufficient
    shear to support organizing clusters of storms. Isolated supercells
    are possible initially, and these storms may pose a risk for
    (mostly) marginally severe hail, before the risk for potentially
    damaging wind gusts become more prominent later this afternoon.

    Areas of deepening convective development are already evident along
    this corridor, and a severe weather watch will probably be issued
    within the next hour or two.

    ..Kerr/Hart.. 07/21/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!qDQnzDMIiLZpNEfavogTXPfSPbV2BTo4M_VDL4jqaP9sZuTYpCe-c5ApxCamRw-AaXSdpsBS$=
    for graphic product...


    LAT...LON 41397389 42227140 41367090 40097343 38967544 38087720
    38937754 39757718 40267570 41397389=20

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