• MESO: Mesoscale Discussion 1099

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Fri Jun 25 22:54:48 2021
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    ACUS11 KWNS 252254
    SPC MCD 252254=20

    Mesoscale Discussion 1099
    NWS Storm Prediction Center Norman OK
    0554 PM CDT Fri Jun 25 2021

    Areas affected...northeast Colorado...northwest Kansas...and central

    Concerning...Severe Thunderstorm Watch 316...

    Valid 252254Z - 260000Z

    The severe weather threat for Severe Thunderstorm Watch 316

    SUMMARY...Thunderstorms continue across many portions of Severe
    Thunderstorm Watch 316. The main threats this evening will be hail
    and strong, gusty thunderstorm winds. The overall severe threat
    should diminish later this evening with the loss of diurnal heating.

    DISCUSSION...Several areas of thunderstorms are ongoing across the
    Severe Thunderstorm Watch: one in northeast Colorado, one across
    central Nebraska, and across northwest Kansas.

    Across central Nebraska, discrete thunderstorms are ongoing along a
    convergence zone associated with, and to the south of, a remnant MCV
    over north-central Nebraska. Despite weak lapse rates, a warm, moist
    boundary layer across the region has allowed surface-based CAPE to
    increase to in excess of 2000 J/kg ahead of the ongoing
    thunderstorms. Given the degree of instability, coupled with
    deep-layer shear around 40 knots, thunderstorms may continue to pose
    a severe threat through the evening. Hail and gusty thunderstorm
    winds would be the main threats. The threat should lessen with time
    this evening as diurnal heating and boundary-layer decoupling reduce surface-based CAPE and the weakening of the convergence zone limits
    forcing for ascent.

    Across northeast Colorado, several areas of linear thunderstorms
    continue to move broadly east toward western Kansas. The strongest
    such storms are currently moving northeast through Cheyenne County,
    Colorado. Additional thunderstorms are moving southeast across Yuma
    County, Colorado, and will enter northwest Kansas shortly.
    Instability here is less than areas farther east given a drying of
    the lower levels. Consequently, however, greater
    temperature-dewpoint spreads should allow for at least some risk for
    strong, gusty thunderstorm outflows. This threat should continue for
    a few more hours before generally weakening later this evening with cooling/decoupling of the boundary layer.

    Across northwest Kansas, thunderstorms have recently developed out
    of the persistent cumulus field associated with a weak convergence
    zone that is apparent on KGLD radar. Here, low-level moisture is
    greater than areas farther east. The result is surface-based
    instability between 1500 and 2000 J/kg. However, effective-layer
    shear is less than across Nebraska given the lessening influence of
    the aforementioned MCV. Current expectation is that these
    thunderstorms should move very little this afternoon until being
    impinged upon by the outflow associated with the thunderstorms
    moving out of Colorado. Given the degree of instability, gusty
    thunderstorm outflows and hail will be possible with the strongest thunderstorms. This threat should diminish with time this evening.

    ..Marsh.. 06/25/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!upxKwyyyyxmIC_NsBHc097s5W1jZ6Q-BfMFTQYI1jy-L8Cb4ZoUe3pTQ8LsQihhfjXDoWNKt$=
    for graphic product...


    LAT...LON 38540405 38860403 38860372 40020369 40000346 40440345
    40440202 40360204 40360134 40700132 40710122 41390125
    41420024 41740023 41749830 41929828 41919781 42119783
    42089736 41769738 41769725 41389723 41459689 41049689
    41049735 40009736 39999791 39589794 39569903 39139905
    39120014 38700013 38690113 38290113 38260204 38620204
    38600317 38520317 38540405=20

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