• DAY1SVR: Enhanced Risks

    From Dumas Walker@21:1/175 to All on Monday, April 01, 2024 08:43:00
    ACUS01 KWNS 011247
    SPC AC 011245

    Day 1 Convective Outlook
    NWS Storm Prediction Center Norman OK
    0745 AM CDT Mon Apr 01 2024

    Valid 011300Z - 021200Z


    Severe thunderstorms are expected today into this evening within a
    broad swath from the southern Plains to the lower Missouri and Ohio
    Valley regions. Tornadoes (a few strong), destructive hail, and
    damaging thunderstorm gusts all are possible.

    The most important mid/upper-level feature for this forecast will be
    a deep, positively tilted, synoptic-scale trough, initially
    extending from the northern High Plains across UT to northern Baja.
    Several shortwave troughs and vorticity lobes will traverse the
    associated cyclonic flow, as the broader trough shifts eastward. By
    the end of the period, the synoptic trough should extend from IA
    across KS and the southern High Plains to far west TX and
    northwestern MX. A lead shortwave perturbation -- evident in
    moisture-channel imagery over the eastern AZ/western NM region and
    southward into adjoining parts of MX -- will eject across the
    southern High Plains today, reaching the TX Panhandle and western OK
    by 00Z. This feature should proceed northeastward to parts of
    northwestern MO and IA by 12Z tomorrow.

    Surface analysis at 11Z showed a frontal-wave low over central KS,
    with warm front to near a line from SZL-STL-ILN. The low should
    migrate along the slowly northward-moving warm front to MO by 00Z,
    with cold front southwestward across northwestern OK and the
    northernmost TX Panhandle. A dryline -- drawn initially from the
    low to the eastern TX Panhandle, near MAF, then southward into
    northern Coahuila -- should shift eastward through the afternoon to west-central/southwestern OK, extending southward across the TX Hill
    Country to near LRD. By 00Z, the warm front -- perhaps modulated on
    the mesoscale by areas of precip -- should extend across northern
    MO, central parts of IL/IN, to southern OH and parts of WV. A
    secondary low may form near the front/dryline intersection over
    western OK. By 12Z tomorrow, an elongated low-pressure area, with
    more than one center, is possible from the main frontal inflection
    over northeastern MO to central IN. The main cold front should
    reach southwestern MO, southeastern OK, northwest TX, and
    southeastern NM. To its southeast, a Pacific front should overtake
    the dryline this evening and overnight, reaching western AR, the
    Arklatex, east TX, and parts of deep south TX by the end of the

    ...Southeastern KS and western Ozarks to central TX...
    Scattered (OK/KS) to isolated (central TX) thunderstorms are
    expected to develop this afternoon along/ahead of the dryline and
    front, quickly becoming severe with all hazards possible. The hail
    threat will be greatest during the first few hours, while tornado
    potential ramps into a probable early-evening peak. Severe
    downdraft gusts also are possible, given the strong available
    buoyancy and fast cell motions expected.

    By late afternoon, much of OK and southeastern KS will reside under
    the left-exit region of a cyclonically curving jet streak, above
    strong low-level moisture transport accompanying a 50-65-kt LLJ.
    Initiation is expected as large-scale ascent preceding the lead
    shortwave starts to impinge upon a favorably heated dryline and
    moist sector, and the basal EML capping layer erodes. This may
    occur earlier over the northern OK/KS part of the outlook near the
    front. The environment will be favorable for frequent large hail
    and occasional significant to giant hailstones from any sustained
    supercells. MLCAPE of 2000-3000 J/kg is possible, amidst 60-75 kt effective-shear magnitudes. Forecast soundings indicate abundant
    inflow-layer moisture content to supply the updrafts, long
    hodographs commonly associated with significant hail (from right- or left-moving storms), as well as significant to giant hail in both
    historic analog soundings and a 2D hail-model.

    Though convective coverage may become densest north of the Red
    River, the potential for longer-lasting discrete modes near and
    south of the Red River conditionally favor isolated extreme hail
    sizes even into north TX. Given mesoscale uncertainties and
    inconsistent convection-allowing model signals regarding initiation
    timing (which influences what low-level shear/hodograph space cells
    will enter) and mature storm duration before upscale merging/linear
    evolution occur, will hold hail probabilities at previous levels for
    now. However, a "hail moderate" may become necessary in this region
    if mesoscale trends and post-12Z/today guidance become better
    focused on timing/density.

    The geometry of the pattern aloft will compel a strong component of mid/upper-level flow parallel to the convective alignment,
    encouraging eventual merging, training, and quasi-linear evolution.
    How long that process will take is uncertain, and the line
    ultimately may backbuild into central TX. Still, with LLJ-expanded
    hodographs and surface-based inflow parcels available in the
    early/mid evening, tornado potential (some strong) should exist with
    any remaining discrete storms, as well as in embedded QLCS
    mesocirculations. Severe potential should ramp down late tonight
    (after about 06Z) over this region, but persist longer in the next

    ...Lower Missouri Valley to Ohio Valley...
    Multiple episodes of strong-severe thunderstorm development are
    expected this afternoon through tonight, each capable of all severe
    hazards. The distribution of severe weather over this corridor may
    be quite non-uniform/clustered, as mesoscale convective processes
    and boundaries evolve. Strong tornadoes may occur over parts of MO
    into central/southern IL while the afternoon/evening CAPE/shear
    parameter space and frontal proximity encourage potential
    development of at least a couple long-lasting supercells.
    Severe to isolated giant hail also is possible, especially from
    discrete supercells the western portion over MO/IL containing
    steepest lapse rates, greatest CAPE, and similarly favorable
    vertical wind profiles as the southern Plains area.

    Moist advection should quickly boost boundary-layer mixing ratios
    and dewpoints today, with surface dewpoints in the 60s common along
    and south of the warm front by midafternoon. Peak/preconvective
    MLCAPE should reach 2000-2500 J/kg south of the warm front over
    parts of MO/IL/IN, diminishing to 1000-1500 J/kg from the
    northeastern KY/southern OH area eastward. Effective-shear
    magnitudes should range from near 60 kt over MO to 40-50 kt in
    eastern parts of the outlook. An MCS may evolve this evening from
    convection over MO and sweep east-northeastward on either side of
    the warm front, reaching parts of IN/OH/northern KY late tonight
    before weakening. Though moving into an airmass that will be
    stabilizing near the surface -- with time and eastward extent --
    such a complex may have enough forced ascent and downward momentum
    transfer behind that to maintain organized wind-damage potential
    over the Ohio Valley tonight.

    ..Edwards/Leitman.. 04/01/2024

    --- SBBSecho 3.20-Linux
    * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (21:1/175)
  • From Dumas Walker@21:1/175 to All on Wednesday, May 22, 2024 07:52:00
    ACUS01 KWNS 220601
    SPC AC 220600

    Day 1 Convective Outlook
    NWS Storm Prediction Center Norman OK
    0100 AM CDT Wed May 22 2024

    Valid 221200Z - 231200Z


    Severe storms with large hail, wind damage and a few tornadoes will
    be likely today across parts of the southern Plains and Ark-La-Tex.
    Isolated severe storms will be possible today from parts of the mid
    Mississippi Valley northeastward into the Ohio Valley and Lower
    Great Lakes.

    ...Southern Plains/Ark-La-Tex...
    West-southwest mid-level flow will be in place over a moist and
    unstable airmass today across much of the southern Plains and
    Ark-La-Tex. At the surface, a cold front will advance southeastward
    into southeast Oklahoma and northwest Texas by afternoon. As surface temperatures and low-level convergence increase along and near the
    front, convective initiation will become likely around midday.
    Numerous thunderstorms are expected to develop and move
    east-southeastward across the southern Plains and Ark-La-Tex during
    the afternoon. The development of a large severe MCS appears likely.

    Ahead of the front, moderate to strong instability is forecast by
    afternoon, with MLCAPE peaking in the 3000 to 4000 J/kg range. In
    addition, moderate deep-layer shear is forecast across much of the
    moist airmass. At 21Z along and near the axis of greatest convective
    potential, forecast soundings from the northern Texas Hill Country northeastward into the Ark-La-Tex, have 0-6 km shear in the 50 to 60
    knot range. This suggests that supercells will be possible, mainly
    early in the event when cells are more likely to be discrete and
    cell interactions are less likely. In addition, forecast soundings
    near the axis of strongest instability, have 700-500 mb lapse rates
    in the 7.5 to 8 C/km range. This environment will be favorable for
    large hail with supercells, with hailstones of greater than 2 inches
    in diameter possible with the strongest of storms. In areas where
    cells congeal into a line, wind damage will become likely. The
    greatest potential will be with the faster-moving bowing segments. A
    few tornadoes are also expected, mainly with supercells and or bow

    The severe threat is expected to persist into the early to mid
    evening, as the linear MCS moves across parts of central and east
    Texas into northern Louisiana.

    ...Ohio Valley/Lower Great Lakes...
    A shortwave trough will move northeastward into the western Great
    Lakes today, as a northeast-to-southwest oriented pre-frontal trough
    advances eastward through the Ohio Valley. A narrow corridor of
    instability will develop near the pre-frontal trough from the mid
    Mississippi Valley northeastward to the lower Great Lakes. As
    surface temperatures warm along the front during the day, isolated
    to scattered thunderstorms are expected to initiate. Multiple
    thunderstorm clusters are expected to develop and move eastward
    through the Ohio Valley during the afternoon. Forecast soundings at
    21Z along the axis of instability from western Kentucky
    northeastward into central Ohio generally have 0-6 km shear in the
    35 to 45 knot range. This, combined with MLCAPE near 2000 J/kg, will
    support a potential for organized severe storms. Although supercells
    will be possible, there may be a tendency for storms to organize
    into short line segments due to flow that will be oriented parallel
    to the convective axis. Wind damage will be the primary threat,
    although hail and a marginal tornado threat will be possible in the
    lower Great Lakes, where deep-layer shear is forecast to be the
    strongest. The severe threat could persist into the early evening,
    as cells move into the central Appalachians.

    ..Broyles/Barnes.. 05/22/2024

    --- SBBSecho 3.20-Linux
    * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (21:1/175)