• MESO: Mesoscale Discussion 0376

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Tue Apr 13 13:29:30 2021
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    ACUS11 KWNS 131329
    SPC MCD 131328=20

    Mesoscale Discussion 0376
    NWS Storm Prediction Center Norman OK
    0828 AM CDT Tue Apr 13 2021

    Areas affected...portions of central/southern LA.

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

    Valid 131328Z - 131530Z

    Probability of Watch Issuance...40 percent

    SUMMARY...Potential will increase through midday for severe
    thunderstorms across the discussion area, with hail initially the
    main concern. Damaging wind may become more of a threat with time
    over south-central LA as the thunderstorms become better-organized
    and shift southeastward.

    DISCUSSION...Scattered thunderstorms in clusters have developed
    during the past hour, mainly over portions of Beauregard, Allen,
    Evangeline, and St. Landry Parishes, with a detached, loosely
    organized arc of weaker convection farther north in central LA. The
    main threat will be large hail for the next couple hours, but late-morning/midday evolution into a cold-pool-driven MCS is
    possible with strong-severe gusts.

    This activity currently is occurring in a zone of elevated warm
    advection and moisture transport, north of a marine/warm front
    analyzed over southeast TX and extreme southern LA near a
    HOU-LCH-HUM line. The 12Z LCH sounding, along that front, sampled
    the upstream inflow layer well for the convection, with steep
    midlevel lapse rates and rich low-level moisture (around 1.75 inch
    PW and surface dew points in the low 70s F). This supports MLCAPE
    around 1000-2000 J/kg, and MUCAPE around 3000 J/kg, combining that
    sounding with objective mesoanalyses. Farther north, modifying the
    sounding, the shallow stable layer at LCH will be more pronounced,
    but with favorable MUCAPE values until buoyancy diminishes in
    central/northern LA. Vertical shear is modest (only around 30 kt effective-shear magnitudes and weal low/midlevel flow), so mode
    should remain mainly multicellular and clustered.

    Though earlier than most progs have depicted during the prior
    overnight period, this activity may be the start of the eventual MCS
    that begins forward-propagating southeastward toward the slowly northward-moving warm front, with progressively more access to
    surface-based effective inflow parcels in that event.

    ..Edwards.. 04/13/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!qMnCHXOxu4SmYCPt4-Yb-dh7V4Fh51sniJ_xwT2yV-WFNKGp2hwLEGYdTx52u32PueslbBPn$=
    for graphic product...


    LAT...LON 30249243 30669329 31179336 31349247 30919157 30199038
    29629064 29689142 30249243=20

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