• MESO: Heavy Rain - floodi

    From Weather Alert@618:250/1 to All on Wed Mar 17 19:12:00 2021
    AWUS01 KWNH 171741
    FFGMPD
    ALZ000-MSZ000-172335-

    Mesoscale Precipitation Discussion 0053
    NWS Weather Prediction Center College Park MD
    139 PM EDT Wed Mar 17 2021

    Areas affected...East-Central TN into Southwest/Central AL

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

    Valid 171735Z - 172335Z

    SUMMARY...Severe supercell thunderstorms will be capable of
    producing some flash flooding this afternoon with localized
    repeating of cell activity and impacts on areas that have recently
    seen heavy rainfall and have saturated soil conditions.

    DISCUSSION...The latest GOES-16 satellite imagery shows convection
    rapidly developing and expanding in coverage across the Deep South
    with visible imagery showing a substantial amount of low-level
    cloud street activity focusing across especially areas of southern
    MS and southwest AL as thinning low clouds allows robust diurnal
    heating to ensue and couples with a moist south-southwest
    low-level jet of 40 to 45 kts for rapid boundary layer
    destabilization.

    The 17Z RAP mesoanalysis suggests a moderate to strongly unstable
    airmass already pooled across the region with MLCAPE values as
    high as 2000 to 2500 j/kg across much of central/southern MS and
    west-central to southwest AL. Meanwhile, there is a significant
    amount of shear in place which is being aided by the approach of a
    strong upper low over the southern Plains. Already strong
    kinematic profiles are favoring warm-sector effective bulk shear
    values of 50 to 60 kts.

    Overwhelmingly, the dominant hazard across the South this
    afternoon and evening will be severe weather, as this highly
    favorable thermodynamic environment couples with strong low to
    mid-level shear profiles over the region for strong and locally
    discrete supercell thunderstorms. Please see the latest SPC Day 1
    Convective Outlook and Tornado Watch #0029 for more details.

    However, there are portions of east-central MS and southwest to
    central AL that will also have a somewhat elevated concern for
    flash flooding if any of these supercell thunderstorms impact or
    perhaps even locally repeat over the same area. Several areas in
    east-central MS in between Hattiesburg and Meridian received as
    much as 5 to 7 inches of rain since early yesterday morning, and
    similar amounts have been noted in parts of southwest to
    south-central AL from west-southwest of Montgomery to the MS/AL
    border.

    The latest HRRR guidance suggests some tracks of supercell
    thunderstorms potentially repeating over the same area and
    supporting as much as 3 to 4 inches of rain with isolate heavier
    amounts going through the late-afternoon hours. This will drive
    some concerns for flash flooding as a result, with a particular
    emphasis on the areas that have seen heavy rainfall over the last
    24 to 36 hours and thus have saturated and highly sensitive soil
    conditions.

    Orrison

    ATTN...WFO...BMX...HUN...JAN...MOB...

    ATTN...RFC...LMRFC...SERFC...NWC...

    LAT...LON 34008656 33238586 32258687 31558815 31258931
    31558986 32118976 32858918 33648806
    $$
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  • From Weather Alert@618:250/1 to All on Thu Mar 25 13:06:00 2021
    AWUS01 KWNH 251258
    FFGMPD
    NCZ000-GAZ000-TNZ000-ALZ000-MSZ000-251856-

    Mesoscale Precipitation Discussion 0065
    NWS Weather Prediction Center College Park MD
    856 AM EDT Thu Mar 25 2021

    Areas affected...northern AL, southern TN, northwest GA

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

    Valid 251256Z - 251856Z

    Summary...A gradual increase in the flash flood risk is expected
    across portions of northern AL, northwest GA and southern TN as
    convection persists across the region through the morning.

    Discussion...Convection is expanding in coverage/intensity this
    morning across portions of northern AL into southern TN. This is
    being driven by very strong low level moisture transport, with the
    bulk of activity focusing on the northern instability/moisture
    transport gradient. The southern extent of the moisture transport
    axis over southern MS/AL will generally remained capped through
    the morning hours...however continued convective development is
    expected further north closer to the area of enhanced low level
    convergence from northern AL into southern TN and far northwest GA.

    The environment is not really conducive for true backbuilding
    cells...however it is favorable for continued upstream convective development...given the persistence of moisture transport and
    available instability...which will then likely track across the
    same areas through the morning hours. It is this multiple rounds
    of cells that will lead to some flash flood risk as the morning
    progresses. Initially the flash flood risk will be isolated...but
    as soils begin to saturate...and additional rounds of convection
    continue...the flash flood risk is expected to increase as the
    morning progresses. Recent HRRR runs seem to have a decent handle
    on the current activity and expected evolution over the next
    several hours. Generally looking at amounts as high as 2-3"
    through 18z over the MPD area. Additional rain after 18z is
    expected...with an uptick in the flash flood risk possible as
    intense convection moves over saturated soils. We will continue to
    monitor the area through the day.

    Chenard

    ATTN...WFO...BMX...FFC...HUN...MEG...MRX...OHX...

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

    LAT...LON 35658564 35658432 35198397 34458483 33758670
    33568748 33968801 34088808 34658823 35168814
    35438709
    $$
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