• MESO: Mesoscale Discussion 0394

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Sat Apr 17 15:18:09 2021
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    ACUS11 KWNS 171518
    SWOMCD
    SPC MCD 171517=20
    LAZ000-171715-

    Mesoscale Discussion 0394
    NWS Storm Prediction Center Norman OK
    1017 AM CDT Sat Apr 17 2021

    Areas affected...Parts of southeastern Louisiana coastal areas

    Concerning...Severe potential...Watch unlikely=20

    Valid 171517Z - 171715Z

    Probability of Watch Issuance...20 percent

    SUMMARY...Increasing, organizing thunderstorm development is
    possible offshore and near southern Louisiana coastal areas through
    1-2 PM CDT, which could pose increasing risk for strong surface
    gusts. While the need for a severe weather watch is still not
    anticipated, trends will continue to be monitored.

    DISCUSSION...Recent new thunderstorm development appears in the
    process of increasing over the northwestern Gulf of Mexico, roughly
    70-90 miles offshore of the upper Texas/southwestern Louisiana
    coast. This may be initially rooted within a zone of weak lower/mid-tropospheric warm advection, to the north of more strongly
    capping warm layers aloft associated with broad mid/upper
    subtropical ridging. However, model output is suggestive that
    forcing for ascent, within the right entrance region of an
    intensifying westerly upper jet (in excess of 120-130 kt around 300
    mb) around the crest of this ridging, could enhance this development
    through early afternoon.

    Ongoing storms appear to be forming above at least a shallow
    near-surface stable layer, to the immediate north of a stalled
    frontal zone which extends east-northeastward, mostly offshore, but
    as far north as southeasterly Louisiana coastal parishes. Based on
    latest objective instability analyses, there may be increasing
    inflow of air emanating from the moist boundary-layer (with surface
    dew points near 70F, supportive of CAPE in excess of 1000 J/kg) to
    the south of the front within the next few hours. Coinciding with
    the strengthening upper forcing, there appears potential for
    substantive further thunderstorm intensification, upscale growth and organization, in the presence of strong deep-layer shear.

    Low-level ambient wind fields are generally weak, but, gradually, convective-scale processes could support increasing potential for
    strong surface gusts, impacting coastal waters and perhaps immediate
    coastal parishes.

    ..Kerr/Dial.. 04/17/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!ufSTaJxoeDLfQ9yw_RrK_nmWJr3t36bjATig5tF5HwPIt-kLeYjRk2bd5DFsVEKmOLmk-uKi$=
    for graphic product...

    ATTN...WFO...LIX...LCH...

    LAT...LON 29589241 29599111 30028965 30058908 30138841 29188812
    28608967 28589144 28689227 29199289 29589241=20



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