• MESO: Mesoscale Discussion 1746

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Monday, December 31, 2018 14:02:34
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    ACUS11 KWNS 311302
    SWOMCD
    SPC MCD 311302
    MSZ000-LAZ000-ARZ000-311500-

    Mesoscale Discussion 1746
    NWS Storm Prediction Center Norman OK
    0702 AM CST Mon Dec 31 2018

    Areas affected...Louisiana and southern Mississippi

    Concerning...Severe potential...Watch possible

    Valid 311302Z - 311500Z

    Probability of Watch Issuance...60 percent

    SUMMARY...Showers and the occasional thunderstorm will continue this
    morning, gradually increasing in coverage and intensity. A damaging
    wind gust or brief tornado may be possible with the strongest
    activity. In the near term, the threat remains too marginal and
    spatially limited for watch consideration. However, later this
    morning a watch may become necessary as convection
    develops/intensifies along the Pacific front.

    DISCUSSION...Showers continue to develop this morning across
    Louisiana and southern Mississippi within a zone of isentropic
    ascent within a warm-conveyor regime. Despite 12Z soundings from
    across southern Louisiana suggesting mixed-layer CAPE around 1000
    J/kg, poor midlevel-lapse rates and tall, skinny CAPE profiles have
    not produced strong enough ascent for charge separation. Even absent
    lightning, ongoing convection is developing within a strongly
    sheared environment, leading to episodic rotation within some of the
    stronger showers. Although low-level buoyancy is somewhat limited,
    near-neutral low-level-lapse rates may support the potential for a
    damaging wind gust or brief tornado through mid morning.

    Later this morning stronger mid-level ascent will begin to overtake
    the Pacific front moving into far western Louisiana at present.
    Despite low-level wind fields remaining somewhat backed behind the
    Pacific front as low-level mass fields respond to stronger surface
    pressure falls across Oklahoma, a modest increase in low-level
    convergence along the Pacific front will combine with the increasing
    synoptic ascent to strengthen convection along the front and support thunderstorm development. Expectation is that a narrow band of
    thunderstorms will develop across portions of central Louisiana and
    lift north-northeast. Again, strong wind fields in the presence of
    modest instability and near-neutral low-level-lapse rates will
    support an isolated damaging wind gust or brief tornado.

    ..Marsh/Grams.. 12/31/2018

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

    ATTN...WFO...JAN...LIX...LCH...SHV...

    LAT...LON 30529296 32909181 33668874 30758965 30529296



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