• MESO: Mesoscale Discussion 1139

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Thu Jul 1 15:45:59 2021
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    ACUS11 KWNS 011545
    SPC MCD 011545=20

    Mesoscale Discussion 1139
    NWS Storm Prediction Center Norman OK
    1045 AM CDT Thu Jul 01 2021

    Areas affected...Portions of far eastern WV...northern/central VA...DC...MD...DE...southeastern PA...and central/southern NJ

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

    Valid 011545Z - 011745Z

    Probability of Watch Issuance...80 percent

    SUMMARY...The threat for scattered damaging wind gusts is expected
    to increase this afternoon, and one or more Severe Thunderstorm
    Watches will likely be needed.

    DISCUSSION...Mid-level west-southwesterly flow over the Mid-Atlantic
    associated with an upper trough/low across Ontario, Quebec, and the
    Great Lakes is not as strong today compared to yesterday. Still,
    about 25-40 kt is present generally around 3-6 km AGL based on
    recent VWP estimates from area radars. An area of precipitation with
    embedded isolated lightning flashes extends from northeastern MD
    into eastern PA as of 1545Z. There is concern that this
    precipitation and its associated widespread cloudiness may tend to
    limit destabilization and steepening of low-level lapse rates early
    this afternoon, particularly across eastern PA into NJ and vicinity.
    Still, there will probably be some clearing behind this initial
    activity, as evidenced by recent cloud breaks across parts of
    south-central PA.

    Better prospects for robust boundary-layer destabilization this
    afternoon will likely be realized across parts of northern/central
    VA into MD and the Delmarva Peninsula where clouds are less
    prevalent. Even though mid-level lapse rates will remain poor,
    around 1500-2000 J/kg of MLCAPE should develop this afternoon across
    this region through diurnal heating of a moist low-level airmass.
    Weaker destabilization, with MLCAPE generally ranging from 500-1500
    J/kg, will probably develop farther north into eastern PA and NJ
    owing to the influence of the ongoing precipitation. Storms will
    probably increase in coverage over the next couple of hours
    along/east of the Blue Ridge Mountains and into south-central PA as
    a weak/decaying MCV moves eastward from WV. 30-40 kt of effective
    bulk shear will likely foster some storm organization, with multiple
    clusters likely moving eastward through the afternoon. The greatest
    threat for scattered damaging wind gusts should develop where
    heating of the boundary layer can steepen low-level lapse rates and
    encourage efficient downdraft accelerations.

    ..Gleason/Thompson.. 07/01/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!v43JShp1LAJaxzVYysPZcydL4reqPW7ZWz9BTB3r29v3ROJEmBPy_vTriPtMiu6vO8Q6sUhu$=
    for graphic product...


    LAT...LON 37917817 37927881 38417897 39087820 39547736 40017643
    40317562 40407487 40207395 39867401 39467418 39187459
    38957478 38727497 38497496 38157508 38007520 37927672

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