• MESO: Mesoscale Discussion 1903

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Tue Oct 26 21:52:43 2021
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    ACUS11 KWNS 262152
    SPC MCD 262151=20

    Mesoscale Discussion 1903
    NWS Storm Prediction Center Norman OK
    0451 PM CDT Tue Oct 26 2021

    Areas affected...portions of southwest Nebraska into central Kansas
    and northwest Oklahoma

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

    Valid 262151Z - 262315Z

    Probability of Watch Issuance...95 percent

    SUMMARY...The potential for severe thunderstorms is increasing
    within the warm sector, ahead of the cold front/dryline. Damaging
    gusts appear to be the main threats though a couple tornadoes and
    instances of large hail are also possible. A WW issuance is expected
    by 23Z.

    DISCUSSION...Latest METAR observations depict the gradual eastward
    movement of the dryline and cold front across the central Plains
    given the approach of a deepening surface low and couple mid-level
    trough. Convective inhibition continues to erode as the boundary
    layer mixes and surface temperatures exceed 80F and dewpoints
    approach the mid 60s F. 8-8.5 C/km mid-level lapse rates are
    overspreading the warm/moist low level airmass, contributing to
    1500-2000 J/kg MLCAPE. Simultaneously, intensifying southerly
    low-level flow with the approaching upper trough will contribute to intensifying deep-layer and low-level shear, with up to 50 kts of
    effective bulk shear and 400 m2/s2 effective SRH expected to develop
    ahead of the dryline in the next few hours, when convective
    initiation will occur.=20

    Meridional/unidirectional tropospheric wind profiles and strong
    forcing for ascent ahead of a merging dryline/cold front suggests
    that transient supercell structures will develop and rapidly merge
    into line segments/squalls. The well-mixed boundary layer and up to
    50 kt 850 mb flow suggests that strong to severe gusts should easily
    reach the surface within and in advance of any well-developed storm
    cores/line segments. Occasional bouts of large hail are also
    expected given the 8+ C/km mid-level lapse rates. Though modest,
    some low-level directional shear is evident in RAP forecast
    soundings, suggesting that the more persistent supercells or
    dominant storms embedded within the squall may acquire occasional,
    strong low-level rotation, with at least a couple tornadoes
    possible. However, the degree of tornado potential will be largely
    dependent on the number of discrete/dominant storms that can form
    and how long they persist, which remains uncertain. Nonetheless,
    organized severe storms are expected in the next few hours, and a WW
    will be issued to address this threat.

    ..Squitieri/Hart.. 10/26/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!q9dYV25Z9s_L1lP2DXlIp8pztx-9-0i7KzWfBmNQ2f3RgT5os-sVeXPLACNfigulLLAuY-to$=
    for graphic product...


    LAT...LON 35769974 36430009 37160018 38090035 39100060 40290093
    40840079 41110059 41200025 40849966 40159898 39439854
    38429798 37499781 36879785 36309814 35839841 35559897
    35589944 35769974=20

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