• MESO: Mesoscale Discussion 1479

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Wed Aug 11 17:01:34 2021
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    ACUS11 KWNS 111701
    SWOMCD
    SPC MCD 111701=20
    MDZ000-VAZ000-DCZ000-WVZ000-111830-

    Mesoscale Discussion 1479
    NWS Storm Prediction Center Norman OK
    1201 PM CDT Wed Aug 11 2021

    Areas affected...Far eastern West Virginia...northern and central Virginia...and portions of Maryland.

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

    Valid 111701Z - 111830Z

    Probability of Watch Issuance...60 percent

    SUMMARY...Storms are expected to move off the higher terrain of the Appalachians and pose a threat for damaging wind gusts this
    afternoon/evening.

    DISCUSSION...Convective initiation has begun in the higher terrain
    in Randolph and Pendleton Counties and vicinity. The airmass is
    still capped in the lower elevations according to SPC Mesoanalysis,
    but with rapid surface heating, expect the remaining inhibition to
    be eroded within the next hour. Visible satellite gives further
    support for this as cumulus have started to form in the lower
    elevations across northern Virginia. The 12Z LWX RAOB showed
    moderately steep mid-level lapse rates (~7 C/km) but very weak
    effective shear (6 kts). These steep mid level lapse rates combined
    with temperatures in the low 90s and dewpoints in the upper 60s has
    combined for MLCAPE around 2000 J/kg per SPC mesoanalysis. Some
    additional heating may bring greater instability and MLCAPE around
    2500 J/kg within the next hour. In addition, the airmass will be
    very supportive for strong downdrafts with DCAPE already around 1200
    J/kg.=20

    Storm organization is not anticipated given the shear profile is not
    forecast to improve much from the LWX 12Z RAOB. However, the
    favorable thermodynamic environment and storm density, which should
    lead to clustering, should be sufficient for a damaging wind threat.


    A watch may be needed in the next 1 to 2 hours.

    ..Bentley/Thompson.. 08/11/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!oOp5hRFqUNvmAZzeDcUcOv75o3RMPn-xvF6g4M3TmokyMzFnZ401hpdxb0wi70J_8HT5-9WC$=
    for graphic product...

    ATTN...WFO...AKQ...LWX...RNK...PBZ...RLX...

    LAT...LON 38657994 39327924 39687826 39707725 39517665 38617656
    37657686 37087780 36997884 37147975 37678024 38657994=20



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