• DAY1SVR: ENHANCED RISK MW

    From Mike Powell to All on Tue May 7 08:10:00 2024
    ACUS01 KWNS 071250
    SWODY1
    SPC AC 071249

    Day 1 Convective Outlook
    NWS Storm Prediction Center Norman OK
    0749 AM CDT Tue May 07 2024

    Valid 071300Z - 081200Z

    ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF INDIANA...OHIO AND NORTHERN/CENTRAL KENTUCKY...

    ...SUMMARY...
    Scattered severe thunderstorms are expected across the Ohio Valley
    today. A few tornadoes (some strong), large to very large hail, and severe/damaging winds all appear possible.

    ...Synopsis...
    A mid/upper cyclone, now occluded at low levels, will meander over
    the northern Great Plains and fill gradually through the period. As
    that occurs, a shortwave trough in its southeastern quadrant over IA
    will eject northward across MN and weaken. A trailing shortwave
    trough -- apparent in moisture-channel imagery over portions of KS
    -- should merge with the trailing portion of the IA perturbation
    then pivot across northern MO, southern IA and the DBQ vicinity,
    reaching northern IL and Lake Michigan by 00Z. That trough then
    should turn eastward through a larger-scale ridge and cross Lower MI
    overnight. South of those troughs, a broad fetch of southwest to west-southwest flow aloft -- with minor and mainly convectively
    influenced perturbations -- should extend from the southern Plains
    to the Ohio Valley.

    At the surface, 11Z analysis depicted a surface low near MBG, with
    occluded front southeastward to southern IA, becoming a cold front
    across western MO, eastern/southern OK, to the TX Permian Basin and southeastern NM. A warm front was drawn across central IL and
    southern IN, with secondary warm front/frontogenesis to its north
    over central IN and southern OH. The western part of both warm
    fronts should consolidate through the day, amid a broader plume of
    warm advection over the Ohio Valley. By 00Z, the cold front should
    reach central IN, southern IL, the eastern Ozarks, southeastern OK, north-central and central TX, with the TX part becoming stationary.
    The front will move northward overnight and become diffuse, amidst a
    broad fetch of southerly flow responding to surface cyclogenesis
    shifting from southeastern KS to northern OK.

    ...Ohio Valley and vicinity...
    A complex and multi-episode severe threat exists today over the
    region. First, an ongoing band of strong/isolated severe
    thunderstorms was apparent across portions of IL, southwestward over southeastern MO and northeastern AR. Though favorable moisture and
    buoyancy exists in the foregoing warm sector (along and south of the
    warm front), height falls aloft and deep-layer lift will be greatest
    over the middle and northern parts, near and just south of the warm
    front and mainly north of the Ohio Rover. What does not overtake
    too much of the warm frontal zone and dissipate in the next few
    hours may reintensify as it encounters diurnally destabilizing low
    levels, related both to low-level theta-e advection and cloudiness-
    restrained surface diabatic heating. At least isolated severe gusts
    would be the main concern with any such convection, which should
    diminish as it moves over/past eastern IN/western OH while
    outrunning already marginally favorable inflow-layer buoyancy.

    The more-substantial severe concern exists for thunderstorms forming
    this afternoon along/ahead of the cold front, then impinging on a
    corridor of favorable heating and warm/moist advection behind the
    morning activity. Surface dewpoints should recover into the mid-
    upper 60s F, beneath a plume of steepening midlevel lapse rates that
    is part of a remnant, somewhat modified EML spreading over the area
    of low-level destabilization. Superposition of these processes
    should yield peak MLCAPE in the 2000-3000 J/kg range over the
    "enhanced" area, narrowing and weakening northward into Lower MI.
    Favorable wind profiles are forecast, with effective-shear
    magnitudes in the 55-65-kt range and large-enough hodographs to
    support 200-400 J/kg effective SRH. To the extent an supercells
    that develop can remain relatively discrete, hodographs in the
    lowest couple km appear favorable for tornadoes (some possibly
    strong). Damaging, large to very large hail also is a concern with
    any such supercells. Buoyancy should be even greater with
    southwestward extent into steeper midlevel lapse rates and greater boundary-layer moisture of the Mid-South, and also southward over
    the Tennessee Valley into AL, but with weaker overall forcing and/or
    vertical shear otherwise, coverage and organization of strong-severe
    convection are likely to be less.

    ...Arklatex to north-central and south-central TX...
    Isolated severe thunderstorms are possible during mid/late
    afternoon. Damaging gusts and large hail would be the main
    concerns. The threat over the area is conditional -- more due to
    weak lift than thermodynamic considerations. Surface dewpoints
    commonly in the 70s F will underlie a deep troposphere and enough
    middle-level lapse rates for MLCAPE in the 3500-4500 J/kg range.
    Weak low-level winds will constrain hodograph size and boundary-
    layer shear. However, enough mid/upper flow remains to support
    around 45-55 kt effective-shear magnitudes, yielding a conditional
    supercell environment. In the absence of meaningful large-scale
    support, and with shallower overall lift near the front/dryline,
    convective coverage over this region is more in question and likely
    isolated. Additional convection may form overnight in a warm-
    advection plume near and southeast of the front, across parts of the
    Mid-South to Arklatex regions. Marginal hail and isolated damaging
    gusts would be the main concerns.

    ..Edwards/Broyles.. 05/07/2024

    $$

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