• MESO: Mesoscale Discussion 0411

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Fri Apr 23 22:37:00 2021
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    ACUS11 KWNS 232236
    SPC MCD 232236=20

    Mesoscale Discussion 0411
    NWS Storm Prediction Center Norman OK
    0536 PM CDT Fri Apr 23 2021

    Areas affected...Parts of east Texas...central Louisiana into
    southwestern Mississippi

    Concerning...Tornado Watch 99...

    Valid 232236Z - 232330Z

    The severe weather threat for Tornado Watch 99 continues.

    SUMMARY...It still appears that the large, evolving cluster of
    thunderstorms will continue to gradually become better organized as
    it spreads into the lower Mississippi Valley through early evening, accompanied by at least increasing potential for damaging wind
    gusts. Trends are being monitored for an additional severe weather
    watch downstream.

    DISCUSSION...A large and sustained cluster of storms continues to
    evolve, with strongest convection along a corridor arcing from
    southeast of College Station, TX into the Fort Polk, LA vicinity.=20
    This appears to be near the northern periphery of warmer and more
    strongly capping mid-level air associated with subtropical ridging.=20
    It is being supported by lift associated with lower/mid tropospheric
    warm advection, beneath a strongly divergent upper flow field
    associated with coupled speed maxima along the subtropical jet.=20
    The forcing, and associated convection are forecast to continue
    developing fairly rapidly east-northeastward into the lower
    Mississippi Valley through 00-02Z.

    Southerly 850 mb flow on the order of 40+ kt appears to be
    supporting moistening inflow, with lifted parcels characterized by
    at least modest CAPE on the order of 500-1000 J/kg. This likely
    will continue, but the the motion of convection may still be
    outpacing the advection of more substantive boundary-layer
    instability, with leading stratiform precipitation tending to
    maintain stable to neutral near-surface lapse rates northeast of

    Still, there has been a strong signal within model output that an
    evolving mesoscale convective vortex will be accompanied by
    intensifying wind fields to 50-70+ kt within the 850-700 mb layer
    across and east of the lower Mississippi Valley this evening. As
    this occurs, the risk for potentially damaging wind gusts seems
    likely to increase somewhere across central Louisiana into
    southwestern Mississippi. A risk for tornadoes may also develop,
    but this will largely hinge on further boundary-layer moistening and destabilization of near-surface lapse rates.

    ..Kerr.. 04/23/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!pf4mBKM9RIvJJbjoL2SG9LV-yOfrVmd4gNeFFSxZXDV1RufE7Zi1SBqGjYMDq0QhVGBt4SYF$=
    for graphic product...


    LAT...LON 31899450 32149338 32039205 31549027 30289163 30689321
    30769383 30449548 30689597 31789509 31899450=20

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