• Catastropic Flooding Ongo

    From Dumas Walker@21:1/175 to All on Fri Sep 27 08:02:00 2024
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    Excessive Rainfall Discussion
    NWS Weather Prediction Center College Park MD
    436 AM EDT Fri Sep 27 2024

    Day 1
    Valid 12Z Fri Sep 27 2024 - 12Z Sat Sep 28 2024

    ...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL FOR THE BLUE RIDGE OF
    NORTH CAROLINA...

    ...CATASTROPHIC FLASH FLOODING WILL LIKELY BE ONGOING FRIDAY MORNING...

    ...Southern Appalachians...

    As the dissipating circulation center of Helene continues to move
    northward today bands of heavy rain will overspread the Southern
    Appalachians focusing some of the highest amounts along the Blue
    Ridge of North Carolina. With likely well over 12 inches of rain
    having fallen in this area prior to the start of the period at
    12Z/8am Friday, this quick hit of as much as 6 inches of additional
    rain in 6 hours will likely push any flooding rivers, streams and
    creeks into major/catastrophic flooding stage. Te High Risk is
    exclusively for Friday morning with the last of Helene's
    rainfall...albeit again some of the heaviest in terms of intensity.
    Once the circulation center passes (and largely dissipates as it
    moves into the mountains), all of the significant rainfall
    associated with Helene will finally be over in this region.

    A broad rain shield will linger over Virginia and West Virginia as
    Helene pivots northward. This part of the region will continue to
    be sensitive to the additional rain and flooding. Despite slightly
    lower amounts of total rain expected, numerous instances of flash
    flooding are expected. The Moderate Risk was maintained for far
    northwest South Carolina, western North Carolina, and portions of
    eastern Tennessee, West Virginia and Virginia.

    ...Ohio, Tennessee, & Mid-Mississippi Valleys...

    The westward portion of Helene's circulation will interact with a
    strong upper level low whose nearly stationary movement has been
    partially responsible for the northward surge of tropical moisture
    associated with the PRE as well as Helene's northward movement.
    Once the circulation center nears Atlanta Friday morning, it will
    turn more northwestward into central Tennessee, then stall out
    there for an extended period of time, maybe even 2 days.

    A fair amount of the tropical moisture will advect westward into
    the Ohio, Tennessee and Mid-Mississippi Valley to help support
    locally heavy rain across Kentucky and Tennessee. The latest model
    guidance and CAMs are depicting a swath of 2 to 4+ inches over
    urban or flood prone areas thus a Moderate Risk was upgraded for
    this period for western and central Tennessee.

    Campbell/Wegman


    Day 2
    Valid 12Z Sat Sep 28 2024 - 12Z Sun Sep 29 2024

    ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
    MIDDLE TO LOWER OHIO RIVER VALLEY...

    Lingering rain associated with the combined upper low and Helene
    will continue mainly across the Ohio Valley into Saturday morning.
    Any flooding impacts may be realized to their greatest extent
    along this portion of the Ohio River on Saturday. A Slight Risk
    remains in effect for portions of the Ohio River Valley although
    with an eastward and southward adjustment to reflect the latest
    trends and observations. Additionally, southern portions of the Northeast/northern Mid-Atlantic were trimmed out of the Marginal
    Risk area due to drier antecedent conditions and not as much
    rainfall from Helene and the frontal system as once expected.

    Campbell


    Day 3
    Valid 12Z Sun Sep 29 2024 - 12Z Mon Sep 30 2024

    ...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
    THE EASTERN Tennessee VALLEY/SOUTHERN Appalachians AND MID-
    ATLANTIC REGION...

    Remnant energy and moisture from Helene will still be present over
    the region with lingering rain over extra sensitive soils. Some
    locations will likely have ongoing riverine flooding and additional
    rain amounts may aggravate the situation. A Marginal Risk for
    excessive rainfall remains in effect from Tennessee and Kentucky to
    points east to Maryland.

    Campbell
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