• MESO: Mesoscale Discussion 1560

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Thu Aug 19 18:01:25 2021
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    ACUS11 KWNS 191801
    SPC MCD 191800=20

    Mesoscale Discussion 1560
    NWS Storm Prediction Center Norman OK
    0100 PM CDT Thu Aug 19 2021

    Areas affected...Northeast Colorado...southwest Nebraska...and far
    northwest Kansas

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

    Valid 191800Z - 192000Z

    Probability of Watch Issuance...80 percent

    SUMMARY...Thunderstorms are expected to initiate by the mid
    afternoon hours (around 20z) across northeast Colorado. A watch is
    likely in the coming hours to address this concern.

    DISCUSSION...Latest GOES visible imagery shows a shallow, but
    growing, field of cumulus north of a surface low and along a
    strongly confluent stationary boundary. The lack of vertical
    development within this field suggests that the environment remains
    capped, which is supported by the latest RAP forecast soundings and mesoanalysis estimates. However, a modest moisture flux to the east
    of the low/surface boundary is allowing MLCAPE to increase into the
    1000-1500 J/kg range. Furthermore, inhibition is forecast to
    continue to weaken through the mid afternoon hours as broad scale
    ascent associated with the approach of the main synoptic wave to the
    west overspreads the region and continued diurnal heating/mixing
    erode the cap. Latest guidance suggests storms may initiate around
    20z across northeast CO roughly within this zone. Effective bulk
    shear values between 30-40 knots will be favorable for storm
    organization and may support a few supercells capable of posing a
    severe wind/hail threat. Initially discrete modes will likely grow
    upscale through the late afternoon due to a strong meridional wind
    component above the boundary layer that is in line with the main
    axis of forcing for ascent. Backed flow in the lowest 1 km is
    supporting effective SRH values on the order of 50-150 m2/s2, which
    suggests a tornado or two is possible - especially with any
    initially discrete cells. An increase in the nocturnal jet this
    evening will boost low-level SRH, but storm mode may hinder the
    tornado threat to a degree. Regardless, severe wind/hail appear
    probable this afternoon, and a watch is likely in the next 1-2 hours
    to address this concern.

    ..Moore/Dial.. 08/19/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!ocDeYQwLLt8S_ODHRRVmFD1p4BZq8BccpaPwdNjs6CHkDvkuJQ4vTXfaVVKYFmKvelsuc6as$=
    for graphic product...


    LAT...LON 38820357 40470366 41610355 41950356 42210328 42320274
    42170206 41760117 41050060 40200039 39510073 39070144
    38620213 38440295 38820357=20

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