• MESO: Heavy Rainfall

    From Weather Alert@21:1/175 to All on Wed Dec 30 23:37:00 2020
    AWUS01 KWNH 302041
    FFGMPD
    TXZ000-310240-

    Mesoscale Precipitation Discussion 0880
    NWS Weather Prediction Center College Park MD
    340 PM EST Wed Dec 30 2020

    Areas affected...South-Central to Southeast TX

    Concerning...Heavy rainfall...Flash flooding possible

    Valid 302040Z - 310240Z

    SUMMARY...Locally heavy showers and thunderstorms, with some brief
    backbuilding of cells, may result in an isolated flash flood
    threat going into the evening hours.

    DISCUSSION...The latest WV imagery shows an upper trough digging
    southeast across the Southwest U.S. which is expected to evolve
    into a rather strong mid-level low center over northern Mexico by
    this evening. Downstream of this over areas of south-central to
    southeast TX, will be increasingly strong deep-layer southerly
    flow which will foster strong warm-air/moisture advection in off
    the western Gulf of Mexico. Along with this, will be rather strong
    upper-level divergence ahead of the trough associated with
    left-exit region jet dynamics approaching the region. Already some
    areas of heavy showers and thunderstorms are situated across
    portions of central to northeast TX as a strong cold front slowly
    settles southeast across the region and coincides with the arrival
    of this more conducive moisture transport and larger scale forcing
    closer to the coastal plain.

    The convective threat though may become a little more focused over
    the next few hours and going into the evening time frame, and
    especially over southeast TX as the front begins to slow down a
    bit more in response to the approaching upstream height
    falls/forcing. The boundary will also be interacting with a
    greater uptick in PWs (reaching 1.25 to 1.5+ inches), stronger
    low-level convergence/Gulf of Mexico inflow, and somewhat greater
    instability with MUCAPE values of as much as 1000 to 1500 j/kg.

    FFG values are quite high across the region, and generally there
    is an ongoing moderate to severe drought. However, the rainfall
    rates should increase somewhat this evening, and will likely get
    up into the 1 to 1.5 inch/hr range occasionally. Several runs of
    the HRRR have been advertising this, and with somewhat better
    instability pooling across the southeast TX coastal plain, the
    heavier rates will likely tend to verify. While these rates are
    not overly high, there will be some potential for the cell
    activity to develop and at least briefly backbuild over the same
    area.

    Going through early evening, some localized pockets of 2 to 3+
    inch rainfall amounts will be possible. Generally any threat of
    flash flooding will be highly localized and confined to the more
    sensitive urban areas.

    Orrison

    ATTN...WFO...CRP...EWX...FWD...HGX...

    ATTN...RFC...WGRFC...NWC...

    LAT...LON 31479563 30769472 29529527 28719694 28869821
    29709845 30239765 30729661
    #
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