• DAY1 Enhanced Risk SC/NC

    From Dumas Walker@21:1/175 to All on Fri Sep 27 08:03:00 2024
    ACUS01 KWNS 271252
    SWODY1
    SPC AC 271251

    Day 1 Convective Outlook
    NWS Storm Prediction Center Norman OK
    0751 AM CDT Fri Sep 27 2024

    Valid 271300Z - 281200Z

    ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM
    EASTERNMOST SOUTH CAROLINA OVER PORTIONS OF SOUTHERN/EASTERN NORTH CAROLINA...

    ...SUMMARY...
    Tornadoes will be most likely through midday and remain possible
    into afternoon across parts of the Carolinas and Virginia.

    ...Synopsis...
    In mid/upper levels, a zonal to west-southwesterly belt of flow will
    persist from the northwestern CONUS and western Canada into central
    Canada, well-removed from a cut-off, cold-core low now evident in moisture-channel imagery over northern MS. This low is expected to
    pivot slowly northeastward into middle TN by 00Z, then wobble
    erratically over that area and/or south-central KY through the night
    as it absorbs the remnant vorticity max from what is now Tropical
    Storm Helene.

    ...SC/NC/VA...
    The path of center of Tropical Storm Helene finally has turned
    northward. See SPC Tornado watch 688 and associated mesoscale
    discussions for near-term coverage of the tornado threat over the
    region. Refer to NHC advisories for the latest track/intensity
    guidance on Helene.

    The NHC forecast shows that the center should bend northwestward
    across southwestern NC, eastern TN and into southern KY through
    tonight, weakening greatly and becoming more closely conjoined with
    the mid/upper cyclone. For several more hours, into at least
    midday, a broad area of strong low-level flow above the surface, and
    related large low-level shear/hodographs, should extend well east
    and northeast of center across the outlook area, superimposed over:

    1. Relatively maximized low-level convergence, in an arc initially
    located over eastern SC into southern NC, preceded by well-backed
    surface winds, and forecast to shift northward to northeastward
    today;

    2. A richly moist, high-theta-e and weak-MLCINH boundary layer
    advecting inland from the Atlantic and characterized by surface
    dewpoints commonly in the 70s F.

    These conditions will yield a favorable environment for tornadoes
    from any supercells that can cross it, whether within or ahead of
    the main spiral/convergence band. The most probable area for
    several supercells to interact with this favorable airmass is over
    the 10%/"enhanced" tornado-risk area, with potential decreasing
    westward and northward from there due to weaker instability.

    Although the supportive low-level airmass will continue to shift
    northeastward over eastern NC and south-central/southeastern VA this
    afternoon, tornado potential will diminish with time from
    midafternoon into early evening. This will occur as convection
    decreases in coverage and intensity across the area due to a
    combination of weakening lift and shear, as the remnants of Helene
    decay rapidly and back well westward away from the area. This
    process will decouple the remaining stronger low-level flow and
    isallobaric forcing away from the most-favorable boundary layer near
    the coast, where hodographs should shrink by the hour this afternoon
    into evening.

    ..Edwards/Broyles.. 09/27/2024

    $$
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