• DAY1SVR: Enhanced Risk SE

    From Dumas Walker@21:1/175 to All on Monday, March 25, 2024 08:41:00
    ACUS01 KWNS 251245
    SPC AC 251243

    Day 1 Convective Outlook
    NWS Storm Prediction Center Norman OK
    0743 AM CDT Mon Mar 25 2024

    Valid 251300Z - 261200Z


    Tornadoes and damaging thunderstorm gusts are possible today through
    tonight from east Texas to Alabama.

    In mid/upper levels, a well-developed synoptic trough extends from a
    cyclone over the central Plains southwestward across far west TX to northwestern mainland MX and central Baja. A series of shortwaves
    behind the leading/synoptic trough will help to maintain larger-
    scale cyclonic flow over much of the western/central CONUS and
    northern MX through the period. However, the 500-mb cyclone should
    move erratically across KS today into this evening, reaching parts
    of northwestern MO, IA and southern MN by 12Z tomorrow. To its east
    and south, a broad, strong fetch of cyclonically curving, roughly
    southwesterly flow aloft will shift eastward from the Southern
    Plains across the lower Mississippi, Tennessee and lower Ohio

    At the surface, 11Z analysis showed a low near CNK, with Pacific/
    leading cold front having overtaken the dryline and drawn through north-central/south-central TX to easternmost Coahuila. A polar
    front was drawn from the low across northwestern OK, the southern TX
    Panhandle and east-central NM. The low should move to west-central
    IA by 00Z, with leading front reaching eastern parts of MO/AR,
    northern LA, extreme southeast TX, and the northwestern Gulf. By
    then, the polar front should extend southward over easternmost parts
    of KS/OK to north-central TX, the northern Permian Basin region of
    TX, and southeastern NM. By 12Z, the low should reach northwestern
    WI, with the fronts essentially merged southward to western KY, and
    the leading boundary from there across southeastern parts of MS/LA.

    ...East TX to AL...
    A swath of precip and embedded convection -- including widely
    scattered thunderstorms -- is apparent along and ahead of the
    Pacific front, from portions of central TX into the Ozarks. Much of
    this activity has exhibited a disorganized, anafrontal character for
    several hours, as the leading boundary continues to progress
    slightly rightward of storm motion. Overall severe potential should
    remain marginal over the next few hours as that general character

    However, severe potential should ramp up from midday onward across
    the outlook area amid favorable/strengthening ambient deep shear.
    Two processes will contribute to increased surface-based
    convective/severe potential along this boundary from midday into
    1. Some slowing of the boundary and decrease in anafrontal
    tendencies as it crosses the lower Mississippi River/Delta region,
    2. The foregoing warm sector becomes substantially more buoyant
    through a combination of warm advection, moist advection and
    diabatic heating of the boundary layer -- especially from a few
    counties north of I-20 southward. Forecast soundings reasonably
    depict a northward-narrowing, triangular wedge of 500-1500 MLCAPE
    shifting eastward over the region ahead of the main convective line.
    While much more uncertain, discrete supercell development may occur
    off the southern/southeastern part of the line, given progged
    decrease in MLCINH in the free warm sector.

    The geometry of the height gradient aloft -- around the southern rim
    of the ejecting cyclone and associated/trailing shortwave trough --
    still will maintain a strongly parallel flow component to the
    primary band of convective forcing, helping to maintain quasi-linear
    mode. However, given the strength of the deep shear (effective-
    shear magnitudes of 55-65 kt), and of the low-level shear/hodographs
    (effective SRH of 250-500 J/kg), the line will encounter in and near
    the "enhanced" area, tornadoes are probable from associated LEWP/bow
    formations and embedded mesovortices, as well as any supercells that
    can mature enough before/during QLCS merger. The parameter space
    will support significant (EF2+ damage potential) tornadoes as well,
    though local storm mode/duration will strongly regulate that threat.
    The QLCS gradually will outpace the favorable inflow-layer
    thermodynamic regime from north-south, as it moves eastward into AL
    overnight, but with southern parts still offering a severe threat.

    ...Lower Missouri Valley region...
    Widely scattered to scattered thunderstorms should form this
    afternoon near the surface low and polar front. Isolated,
    marginally severe hail or gusts may be noted, and a tornado is

    The airmass between the leading and polar fronts will remain
    somewhat moist, with surface dewpoints in the 50s F over much of the
    region. Diabatic heating and warm advection will contribute some
    low-level destabilization, though its duration and strength will be
    limited within a narrow corridor northwest of the cloud/precip
    shield from the aforementioned main convective band. However,
    large-scale lift preceding the ejecting mid/upper-level low and
    trough should lead to cold air aloft (e.g., 500-mb temperatures
    around -19 to -22 deg C), steepening low/middle-level lapse rates
    and decreasing MLCINH through much of the afternoon. This should
    support MLCAPE around 500 J/kg, with strong deep/speed shear and
    potential for vorticity-rich low-level boundaries to augment
    shear/hodographs locally. Convection should weaken soon after dark.

    ..Edwards/Wendt.. 03/25/2024

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  • From Dumas Walker@21:1/175 to All on Monday, March 25, 2024 13:00:00
    ACUS01 KWNS 251607
    SPC AC 251605

    Day 1 Convective Outlook
    NWS Storm Prediction Center Norman OK
    1105 AM CDT Mon Mar 25 2024

    Valid 251630Z - 261200Z


    Tornadoes and damaging thunderstorm gusts are possible today through
    tonight from east Texas to Alabama.

    ...ArkLaMiss Region...
    Few changes have been made to the ongoing forecast. A large upper
    trough is present today over the western states, with the primary
    cold front sagging southward from east TX into western AR.
    Low-level moisture return has been slow ahead of the front over much
    of the lower MS Valley due to easterly trajectories. However,
    mid/upper 60s dewpoints are finally spreading inland into southern
    LA. This trend will continue through the afternoon with ample
    moisture expected into the southern half of MS by evening.
    Increasing moisture and at least broken sunshine should lead to
    sufficient destabilization for thunderstorm intensification by
    mid-afternoon along/ahead of the front over central LA. These
    storms will track northeastward toward central MS by early evening,
    then into western AL after dark. Forecast soundings suggest poor
    lapse rates in the lower troposphere which may limit updraft
    strength and overall severe risk. However, very strong low-level
    shear will promote supercell/bowing structures. Damaging winds and
    a few tornadoes (possibly strong) continue to be the concern this
    afternoon and evening.

    The primary surface low is currently over eastern KS and will track
    into western IA this afternoon. Visible satellite imagery shows a
    region of mostly clear skies in the warm sector of the low, leading
    to steepening low-level lapse rates and marginal CAPE. Most 12z CAM
    guidance develops a few low-topped showers or perhaps thunderstorms
    late today along the front as it moves into this area. The most
    robust cells might produce gusty winds, funnel clouds, or perhaps a
    tornado for a few hours this afternoon.

    ..Hart/Thornton.. 03/25/2024

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