SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0750 AM CDT Mon May 06 2024
Valid 061300Z - 071200Z
...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
WESTERN...CENTRAL AND NORTHERN OKLAHOMA TO SOUTH-CENTRAL KANSAS...
...SUMMARY...
A regional outbreak of severe weather with multiple strong,
long-tracked tornadoes, as well as very large hail and severe
thunderstorm gusts, is expected over parts of the south-central
Plains from this afternoon through evening.
...Synopsis...
In mid/upper levels, a strong synoptic-scale trough was evident in
moisture-channel imagery from the northern Rockies, through a low
over northeastern UT, then southward to the international border
near the AZ/NM line. The main 500-mb low should pivot northeastward
toward the Black Hills and deepen by 00Z, with trough northwestward
over central MT and southward across eastern parts of CO/NM.
A basal shortwave trough -- now from central CO to the Four Corners
area -- should swing northeastward then northward, reaching southern
SD, western NE and eastern CO by 00Z. This perturbation then should
shift northeastward, possibly merging with convectively generated
vorticity over NE and SD this evening and tonight, and reaching
eastern SD, southwestern MN and IA by 12Z. A weaker, but still
influential perturbation -- now over parts of southern NV/northern
AZ -- should make a net eastward shift to parts of northeastern NM
and the TX Panhandle by 00Z, reaching southern KS and northern OK by
12Z. Associated substantial height falls and DCVA should remain
over and north of the Red River Valley through this evening.
At the surface, an elongated area of low pressure was analyzed on
the 11Z chart over eastern WY, with Pacific cold front across
eastern CO and northeastern/north-central NM. A dryline extended
from the front over southeastern CO to eastern NM and the TX
Trans-Pecos region, and should mix eastward to southwestern KS,
eastern OK/TX Panhandles, and west-central/southwest TX by late
afternoon. The cold front should overtake the dryline across the
central Plains through the afternoon, then over OK overnight. A
developing/synoptic warm-frontal zone was apparent from southeastern
WY across central KS to southern MO, and should move northeastward
to the lower/mid Missouri Valley through the period. The southern
warm front -- demarcating the northern rim of a richly moist Gulf
airmass from outflow-modified air, was drawn near the Red River from
the Arklatex to the southeastern TX Panhandle. This boundary will
shift northward through OK and much of KS today while becoming
diffuse, and possibly catching up to the northern warm front.
...OK, Southern KS, Red River region...
Thunderstorms are expected to develop by mid/late afternoon along
and ahead of the dryline, near the eastern TX Panhandle/western OK
line or 100W longitude into southern KS, then strengthen quickly to
severe levels as they move eastward. Given the already very
favorable parameter space by late afternoon, and increasingly so
into early/mid evening, the concern is high for at least a few
cyclic, tornadic supercells producing multiple significant tornadoes
along potentially long paths. The threat for such tornadoes, as
well as very large/destructive hail, will be maintained well into
the late evening, and may even increase as hodographs further
enlarge beneath the LLJ. Some uncertainty lingers as to how many
such supercells will track across the outlook area, but given the
unusually favorable environment and increasing confidence, a "high
risk" outlook is warranted for areas between roughly the I-40
corridor in OK and the US-54/500 corridor in southern KS.
Compared to farther north in KS, the environment will feature
slightly stronger CINH, very rich low-level moisture (dewpoints
commonly upper 60s to low 70s F), lack of frontal forcing (mainly
dryline instead), and more orthogonal mean-wind/deep-shear vectors
relative to the boundary. The 12Z FWD sounding sampled the richly
moist and deep boundary layer that will be shifting northward across
OK today, with mean mixing ratio of 15 g/kg. As low clouds erode in
the moist sector from west-east, diabatic heating will boost MLCAPE
into the 2500-4000 J/kg range over western/central OK and southern/
central KS, and contribute to greater potential for discrete
supercells to develop and last a few hours before potential major
upscale evolution to lines or clusters this evening.
Hodographs will be favorable for tornadoes soon after initiation,
and enlarge further ahead of the activity with time. Effective SRH
commonly around 200-300 J/kg is expected late this afternoon and
300-500 J/kg after 00Z, amidst strengthening LLJ and deep shear
(effective-shear magnitudes reaching 45-60 kt). Effective-layer STP
in the 5-12 range may be realized for a few hours this evening
across parts of OK and southern KS. Stronger MLCINH and weaker
large-scale support will contribute to lesser storm coverage with
southward extent over southern OK, though significant tornadoes and
damaging hail may be possible from any that form.
The corridor of favorable buoyancy will enlarge eastward this
evening with continued moisture transport/advection, helping to
maintain surface-based effective-inflow parcels well eastward into
the Ozarks and vicinity to maintain eventual upscale growth,
possibly linking with the southern part of QLCS activity sweeping
across the Missouri Valley region.
...Central Plains...
Thunderstorms should develop as early as midday to early afternoon
over portions of western KS and southwestern NE, where CINH will be
weakest, as the southern part of the front overtakes the dryline and
impinges on a rapidly destabilizing/moistening sector to the east.
Initial supercell mode is possible, with tornadoes (some strong),
large to very large hail and damaging gusts all possible. With time
this afternoon into evening, a more quasi-linear storm mode may
evolve as the influence of frontal forcing increases, versus some
component of flow across the boundary. As that occurs, tornadoes
still will be possible, and the hail threat will transition to
severe wind with eastward extent. Some significant (near 75 mph or
higher) gusts will be possible as the momentum of stronger flow
aloft gets transported to the surface, with increasing forced ascent
along the leading edge of the complex. 60s F surface dewpoints will
overspread a northward-narrowing sector across much of KS and NE
today, contributing to peak/preconvective MLCAPE increasing into the
2000-3000 J/kg range, as deep shear strengthens, and hodographs
extend, while maintaining favorable curvature.
...Northern Plains...
From central NE northwestward, the prefrontal corridor of favorable
moisture and diurnal destabilization will become quite narrow.
Nonetheless, it should support scattered thunderstorms in northward-
shifting plume, curving from the western Dakotas (and perhaps parts
of extreme northeastern WY and southeastern MT) southeastward to
central NE, and connecting to the northern part of the central
Plains severe threat. With strong large-scale lift, cooling aloft,
rapidly weakening MLCINH, and robust low-level mass response/shear
expected ahead of the ejecting shortwave trough, confidence is
growing that an arc of strong-severe thunderstorms will develop,
offering large hail, severe gusts and at least marginal tornado
potential. Even with 50s to low 60s F surface dewpoints and limited
time for substantial diabatic heating, the net steepening of low/
middle level lapse rates should support peak MLCAPE near or slightly
above 1000 J/kg. Deep shear may not be particularly intense in a
regime of strongly difluent flow aloft, but still should be adequate
for supercell potential given large lowest-km hodographs possible,
and effective SRH in the 150-300 J/kg range. Severe potential
should diminish after about 00Z.
...West-central/southwest TX...
Isolated thunderstorms are possible in mid/late afternoon along/
ahead of the dryline over northwest to southwest TX. Although
large-scale/mid-upper forcing will be negligible, any pockets of
relatively persistent/maximized low-level lift associated with
solenoidal processes on the dryline may persist enough to initiate
convection. Mid/upper 60s to low 70s F surface dewpoints and steep
low/middle-level lapse rates will contribute to 3000-4000 J/kg
MLCAPE amidst enough deep shear for supercells. A conditional
significant-hail and marginal tornado threat exists with sustained
supercell(s) -- if any can form. Coverage concerns preclude more
than marginal categorical outlook at this time.
..Edwards/Broyles.. 05/06/2024
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