• MESO: Mesoscale Discussion 1734

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Thursday, December 27, 2018 10:10:39
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    ACUS11 KWNS 270910
    SWOMCD
    SPC MCD 270909
    LAZ000-TXZ000-271115-

    Mesoscale Discussion 1734
    NWS Storm Prediction Center Norman OK
    0309 AM CST Thu Dec 27 2018

    Areas affected...portions of southeast Texas and
    southwestern/west-central Louisiana.

    Concerning...Tornado Watch 446...

    Valid 270909Z - 271115Z

    The severe weather threat for Tornado Watch 446 continues.

    SUMMARY...A band of strong/locally severe thunderstorms will
    continue to offer a threat for sporadic damaging gusts across parts
    of southeast Texas, and a tornado or two cannot be ruled out given
    the favorable environment. A new watch may be needed before the 10Z
    expiration time of this one, to cover the potential eastward shift
    in severe potential across the Sabine River area.

    DISCUSSION...Surface mesoanalysis showed a warm front erratically
    winding across southeast Texas from south of LFK to between HOU-BPT,
    across the GLS area then eastward over LA shelf waters. The
    relatively cold shelf waters are influencing surface temps between
    BPT-GLS and south of LCH. However, a combination of warm advection
    over that shallow layer and vertical mixing should effectively
    re-form the warm front over the lower Sabine River region during the
    next few hours. This process will expand the modified marine
    sector, with at least marginally surface-based effective-inflow
    parcels, eastward ahead of the QLCS described next.

    A well-developed QLCS was evident at 09Z from just west of ELD in
    southern AR southwestward across the SHV area to near UTS and the
    middle Texas Coastal Plain. A newer line of convection has formed
    from its intersection with the original QLCS over eastern
    Fayette/Colorado Counties south-southwestward across Victoria
    County, with the QLCS weakening to its west. The combined
    convective band is expected to continue moving eastward across and
    out of the remaining watch area, into a regime characterized by
    MLCAPE 1000-2000 J/kg. MLCINH increase with eastward extent into LA
    but also should decrease with time, as the warm frontal zone
    repositions. 50-kt effective-shear vectors and large SRH, as
    sampled by VWP hodographs, will support severe potential in the
    QLCS, as well as with any relatively discrete/sustained cells that
    can be maintained to its southeast, closer to the coast.

    ..Edwards.. 12/27/2018

    ...Please see www.spc.noaa.gov for graphic product...

    ATTN...WFO...LCH...SHV...HGX...

    LAT...LON 29759653 31359451 31649303 30919247 29749305 29759379
    29669385 29689404 29479454 29389470 29349471 29079514
    29259615 29759653



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