• MESO: Mesoscale Discussion 1668

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Wed Sep 1 15:09:05 2021
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    ACUS11 KWNS 011503
    SPC MCD 011503=20

    Mesoscale Discussion 1668
    NWS Storm Prediction Center Norman OK
    1003 AM CDT Wed Sep 01 2021

    Areas affected...northern Virginia into southeast Pennsylvania and
    New Jersey

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

    Valid 011503Z - 011730Z

    Probability of Watch Issuance...95 percent

    SUMMARY...Storms are likely to increase in coverage and intensity
    near a front from northern Virginia into New Jersey. Damaging winds
    and a few tornadoes appear likely.

    DISCUSSION...Surface analysis shows a low over eastern WV with a
    front extending east/northeastward into southern NJ. Extensive
    clouds exist over much of the region, but relative clearing exists
    across eastern NC and VA toward the Delmarva. The strongest
    instability is coincident with the mid 70s F dewpoints near the zone
    of clearing. While temperatures aloft are warm, this is still
    resulting in substantial instability.

    Low-level shear is currently maximized along and just north of the
    stationary front from southern PA into NJ, as well as along an axis
    from the WV Panhandle southward across west-central VA. 0-1 SRH
    values up to 100 m2/s2 exist in the higher theta-e air mass, which
    is sufficient for a tornado risk.

    As the low continues slowly northeastward, and warm advection
    persists near the rain-reinforced stationary front, effective SRH is
    expected to concentrate from northern VA across MD, southeast PA and
    NJ. Showers now forming along a line from central VA into northeast
    NC near the instability gradient are expected to gradually deepen,
    and a couple supercells may evolve out of this line of convection.
    Otherwise, storms are likely to gradually increase in coverage and
    intensity east of the low as it shifts into southeast PA and NJ be
    evening. Both damaging winds and few tornadoes will be possible. In
    addition, the PA/NJ portion of the front is expected to shift north,
    and this may bring the severe risk toward Long Island this evening.

    ..Jewell/Grams.. 09/01/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!uv91VlF52hcrFBzs7qu5PHPy4IohmEJqhhehZPaMAhwzbnFWMi9KPPTDIryO7nu8_P5ohyKH$=
    for graphic product...


    LAT...LON 38497497 37957521 37547557 37227697 37237744 37497769
    38197791 38667826 39047818 39857665 39987619 39987589
    39927549 39687513 39357477 39027478 38847497 38497497=20

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