• MESO: Mesoscale Discussion 1675

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Wed Sep 1 22:40:29 2021
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    ACUS11 KWNS 012240
    SWOMCD
    SPC MCD 012239=20
    SDZ000-NEZ000-020045-

    Mesoscale Discussion 1675
    NWS Storm Prediction Center Norman OK
    0539 PM CDT Wed Sep 01 2021

    Areas affected...western Nebraska into central South Dakota

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

    Valid 012239Z - 020045Z

    Probability of Watch Issuance...60 percent

    SUMMARY...Showers and thunderstorms will develop and increase in
    coverage this afternoon and evening. Large hail and damaging
    thunderstorm winds will be the primary hazard, although a tornado or
    two will be possible through mid-evening. A watch may become
    necessary and conditions will be monitored.

    DISCUSSION...A moist, upslope regime persists across the region to
    the north of a lee cyclone across northeast Colorado. To the north
    of this lee cyclone, an inverted trough stretches from northeast
    Colorado into southwest South Dakota. Area point-forecast soundings
    indicate a pronounced warm nose in the 600-700 millibar layer, which
    has provided a lid on convective initiation this afternoon. However,
    continued heating and increasing large-scale ascent associated with differential vorticity advection tied to the mid-level remnants of
    tropical cyclone Nora should help to cool this warm layer through
    the afternoon and evening. Additional, lower-level, forcing for
    ascent will increase in response to increasingly warm, moist
    advection on the nose of a strengthening southeasterly low-level jet
    to the northeast of the lee cyclone across northeast Colorado. The
    result should be an increase in showers and thunderstorms this
    afternoon and evening within an environment characterized by
    most-unstable CAPE values between 1500-2500 J/kg and effective-layer
    shear of 35-40 knots. The most likely severe hazard from these
    storms would be large hail and strong, gusty thunderstorm winds,
    although a tornado or two cannot be ruled out this afternoon and
    early evening, especially in the presence of low-level boundaries
    that may provide an enhanced vorticity reservoir.=20

    A watch may become needed later this afternoon and conditions will
    continue to be monitored.

    ..Marsh/Guyer.. 09/01/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!uIC4HXlgK3HyK7MGn_bkrGeip4wqn4Im8C3l6N4Vw1A8grpmUlk897Nn2uCfAaVhzLFOZdv9$=
    for graphic product...

    ATTN...WFO...ABR...LBF...UNR...CYS...

    LAT...LON 42790364 44820165 45340078 45239970 44399957 43210043
    41670264 41690369 42790364=20



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