• Heavy Rain/Flood Appalach

    From Mike Powell@618:250/1 to All on Tuesday, September 24, 2024 12:44:00
    AWUS01 KWNH 241738
    FFGMPD
    VAZ000-NCZ000-WVZ000-SCZ000-GAZ000-TNZ000-KYZ000-242300-

    Mesoscale Precipitation Discussion 1047
    NWS Weather Prediction Center College Park MD
    138 PM EDT Tue Sep 24 2024

    Areas affected...Southern to South-central Appalachians...

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

    Valid 241735Z - 242300Z

    SUMMARY...Scattered cells ahead of main convective lines may
    pre-soak rugged areas with spot of 1-2.5" resulting in scattered
    possible flash flooding.

    DISCUSSION...GOES-E visible imagery shows a fairly clear skies
    over the Appalachians across S WV/SW VA into E TN/W NC and far
    upstate SC. Temperatures have risen to upper 70s/low 80s with
    well above average low level moisture having filtered through the
    range with Tds in the mid to upper 60s. As such, the area has
    become fairly unstable with 1250-1750 J/kg of MLCAPE. Solid
    25-40kts of southwesterly 850-700mb flow has been advecting
    increasing moisture through the lowest levels to further moisten
    the lower column with total moisture reaching 1.5" even into the
    higher slopes with some suggestion of 1.7" starting to reach
    eastern TN through the Cumberland Plateau.

    While main northern stream trough remains well west over the
    Midwest digging into the Tri-Rivers area of W KY, a subtle
    southern stream wave can be seen sliding through E TN moving
    generally parallel to the slopes. This forcing combined with
    low-level convergence from approaching pre-frontal convective line
    out of KY, is starting to spark increasing TCu and incipient CBs
    across the clearer skies downstream. More mature cells along the
    pre-frontal trough as well as very near the shortwave lifting
    north will likely continue to enhance with cells capable of
    1.25-1.75"/hr rates. While cell motions will likely limit overall
    totals to about 30-60 minutes, it is the pre-cursory cells that
    given solid instability and updraft strength may be capable of a
    similar 1-2"/hr total prior to the main forcing lines that may
    result in spots of 1.5-2.5" totals over a 3 hour period as they
    repeat or at time merge with the cells in the effective warm
    sector ahead of the line.

    Hydrologically, the rugged area has naturally lower FFG values at
    1-1.5"/hr and 1-2"/3hr which suggest either slower moving
    pre-cursory cells or the stronger forced lines will have a solid
    potential of being exceeded. The scattered and transitory nature
    is likely to result in localized scattered incidents of flash
    flooding given 1.5-2.5" totals through 00z.

    Gallina

    ATTN...WFO...GSP...JKL...LWX...MRX...RLX...RNK...

    ATTN...RFC...LMRFC...MARFC...OHRFC...SERFC...NWC...

    LAT...LON 38798028 38517956 37897963 37337997 36208103
    35368190 34978242 34898304 35248336 35868325
    36378346 36968305 37638230 38528109
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