• MESO: Mesoscale Discussion 0423

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Sat Apr 24 17:30:34 2021
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    ACUS11 KWNS 241730
    SPC MCD 241729=20

    Mesoscale Discussion 0423
    NWS Storm Prediction Center Norman OK
    1229 PM CDT Sat Apr 24 2021

    Areas affected...portions of far northeast Louisiana...southeast Mississippi...southwest Alabama

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

    Valid 241729Z - 241930Z

    Probability of Watch Issuance...60 percent

    SUMMARY...An increasing severe threat is anticipated over the next
    couple of hours. Large hail and damaging wind gusts will be the
    primary threat with the stronger storms. A Severe Thunderstorm Watch
    may be needed soon for parts of this area.

    DISCUSSION...Clearing skies and resultant ample insolation have
    supported low-level airmass modification over the past few hours
    across portions of the central Gulf Coast in the wake of a passing
    MCS. Current visible satellite imagery depicts an expanding CU field
    within a region of broad low-level confluence across eastern LA into
    southern MS and AL. Latest high-resolution guidance consensus
    depicts convective initiation occurring around 18-19Z. Modest
    mid-level lapse rates (6.5-7 C/km) advecting eastward atop mid 60s
    to near 70F dewpoints, along with the aforementioned heating,
    supports 1000-2000 J/kg MLCAPE in the modified central Gulf Coast
    airmass. While ample wind speed increases with height will support
    50-70 kts of effective bulk shear, tropospheric winds appear nearly unidirectional, and are oriented roughly parallel to the confluence
    zone. As such, semi-discrete cellular clusters and linear segments
    are expected to be the predominant mode of convection, though brief,
    transient supercells are possible.=20

    The strong deep-layer shear and modest lapse rates will promote
    severe hail with any of the more intense, sustained storms. Adequate boundary-layer mixing in advance of developing storms may also
    steepen low-level lapse rates sufficiently enough to support a few
    damaging gusts as well. With an increase in storm coverage expected
    to take place in a couple of hours, a Severe Thunderstorm Watch
    issuance may be necessary to address the increasing severe threat.

    ..Squitieri/Hart.. 04/24/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!qtUg-a4SRUGeL42ljwzl71Krx5kqhz2eVH-p1xItrQDjXVvLYMAfx9pnycKvJXRewanXe0ch$=
    for graphic product...


    LAT...LON 30698723 30138797 29868888 29788951 29909039 30089074
    30229086 30379092 30489095 30589094 31099061 31909009
    32318922 32528878 32548859 32578829 32418776 32158718
    31908678 31578662 31228679 30698723=20

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