• MESO: Mesoscale Discussion 1567

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Fri Aug 20 18:52:03 2021
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    ACUS11 KWNS 201851
    SPC MCD 201851=20

    Mesoscale Discussion 1567
    NWS Storm Prediction Center Norman OK
    0151 PM CDT Fri Aug 20 2021

    Areas affected...Eastern Nebraska western Iowa and far southeastern
    South Dakota

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

    Valid 201851Z - 202015Z

    Probability of Watch Issuance...40 percent

    SUMMARY...Convective development is expected ahead of a cold front
    by early afternoon across northeastern Nebraska. Bands of storms
    capable of damaging winds/hail are expected and a weather watch is
    likely needed later this afternoon.

    DISCUSSION...As of 1840 UTC, regional WV imagery showed a large
    negatively tilted upper low and developing 40 to 50 kt jet streak
    across the western High Plains. At the surface, a 1004 mb low was
    located along the ND/SD border with a cold front trailing south
    through east-central Nebraska. There, latest visible imagery showed
    agitated cumulus and weak convective cells ongoing along and ahead
    of the front.=20

    As surface heating continues ahead of lift from the advancing
    trough, remaining inhibition observed on the 18z OAX sounding will
    erode and showers/thunderstorms will continue to form along the
    front early this afternoon. With dewpoints in the low 70s F, SPC
    mesoanalysis shows MLCAPE of 2000-3000 J/kg supportive of strong
    updrafts. Regional soundings and VADS show 30-40 kts of effective
    shear near and behind the front supportive of organized
    lines/clusters and initial supercell structures. Strong forcing
    along the fast moving front and will favor rapid upscale growth of
    any storms that do develop suggesting the main threats will be
    damaging winds and some hail.=20

    Convective trends and Hi-res guidance suggest initiation of
    near-surface based storms is likely by as early as 1930-20z but,
    uncertainty remains relatively high on the initial organization of
    any storms that do develop. Stronger mid-level flow is somewhat
    lagging behind the fast moving surface features suggesting storms
    may initially be slow to organize. While the potential for severe
    winds and hail does appear probable given the favorable parameter
    space, the exact timing for a convective watch is uncertain.

    ..Lyons/Guyer.. 08/20/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!qQvEuIbrHFZmEGKKvwKsQsMm-EoYV4cGXJw8-ayg8oqJ0WVaVGBEgoO2A4HzmI7NI2NQPFTr$=
    for graphic product...


    LAT...LON 42869758 43289717 43349674 43349620 43379569 43229529
    42989510 42589498 42159491 41749490 41279501 41009519
    40739551 40419593 40059663 40149732 40429752 40769774
    41219786 41759776 42869758=20

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