ACUS01 KWNS 241256
SWODY1
SPC AC 241255

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0755 AM CDT Fri May 24 2024

Valid 241300Z - 251200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS MORNING
OVER PARTS OF EASTERN IOWA AND NORTHERN ILLINOIS...AND THIS
AFTERNOON TO EVENING OVER PARTS OF EASTERN OKLAHOMA AND
NORTH-CENTRAL/CENTRAL TEXAS...

...SUMMARY...
Enhanced threat corridors exist for severe thunderstorm gusts this
morning from eastern Iowa over northern Illinois, and hail (some
very large) this afternoon and evening from eastern Oklahoma to
north Texas.

...Synopsis...
In mid/upper levels, a progressive shortwave train should continue
within a belt of mostly westerly flow aloft over the CONUS. The
strongest of these shortwave troughs is evident in moisture-channel
imagery over the northern Great Plains, with an embedded 500-mb low
over northwestern SD. The low should follow a cyclonically curving,
net northeastward path to the northeastern corner of ND by 00Z, with
trough roughly southward along the western border of MN then over
eastern NE. By 12Z tomorrow, the CONUS part of the trough should
arc from western Lake Superior across eastern WI and northern IL.
Over the Southeast, a broad area of difluent mid/upper flow is
expected, with numerous embedded vorticity lobes (some convectively
generated or enhanced). Fairly unperturbed west-southwesterly flow
is expected from the Arklatex region across the southern Plains and
Desert Southwest, downstream from a trough off coastal CA.

The surface analysis at 11Z showed a low over southeastern ND, with occluded/cold front arching across southwestern MN, western IA,
east-central KS, west-central OK, TX between PVW-LBB, and
northeastern NM. A warm front was drawn from the leading edge of a
severe MCS over eastern IA, southeastward across central IL. The
low should occlude and shift northward over southeastern MB through
the period. By 00Z, the frontal triple point should reach southern
WI, with cold front across western IL, southwestern MO, southeastern
OK and north-central to west-central TX, becoming a warm front over east-central/northeastern NM. The warm front will move
northeastward to southern WI and southwestern Lower MI, though its
definition may be compromised by the effects of MCS activity. A
dryline was apparent from its frontal intersection over northwest TX south-southwestward to the Big Bend region. This boundary will mix
eastward today while the front overtakes it from the north, and
should reach the eastern Edwards Plateau/western Hill Country by
late afternoon.

...Southern Plains to Mid-South...
Scattered thunderstorms -- including supercells -- are expected to
develop near the front this afternoon, to the east and northeast of
the dryline. Dryline storm-initiation potential is more conditional
and isolated. Once development occurs, updraft growth and storm
evolution may occur very rapidly, given the strong surface heating,
abundant moisture (70s F dewpoints common), steep deep-layer lapse
rates and intense buoyancy (4000-5000 J/kg MLCAPE) that should
develop.

Low-level flow and hodograph size will be modest, amidst a lack of
substantial mid/upper-level perturbations to force greater mass
response. However, ambient mid/upper winds will be strong enough to
support supercells (left- and right-moving), with effective-shear
values near 50 kt. Large to very large hail should be common in the
first few hours after initiation, and locally severe gusts are
expected as well. Airmass recovery is possible into southeastern
and east-central OK in the zone of warm/moist advection ahead of the
front, and behind last night's southeastern OK activity. A
relatively dense and enhanced concentration of hail potential from
eastern OK into north-central TX is expected, with hailstones
greater than 2 inches in diameter likely, and some hail perhaps
exceeding 3 inches. Otherwise, deep, precip-loaded downdrafts will
provide most of the wind potential early, with some upscale
clustering and cold-pool aggregation possible to maintain damaging-
wind potential into late evening, before activity generally weakens.

...Midwest...
Enhanced potential for severe gusts, along with a risk of a few
brief/embedded tornadoes, may persist for a few more hours with an
ongoing complex of thunderstorms crossing portions of eastern IA and
northern MO, as this activity moves into IL and perhaps southern WI.
A well-developed rear-inflow jet of 60-80 kt has been sampled by DMX
radar VAD wind profiles. The northern part of the complex is
expected to weaken as it penetrates deeper into the cool sector
(north of the warm front), while the middle part may persist for
several hours near the front and across IL. See SPC Severe
Thunderstorm Watch 300-301 and related mesoscale discussions for
near-term details.

The outflow boundary from this complex was analyzed ahead of the
cold front across parts of northwestern MO into northeastern KS, and
should be laid down through the remainder of the morning across the
rest of northern MO and parts of northern IL. Given the deep and well-organized nature of its cold pool, severe probabilities may be
more associated with the present activity. Later development
becomes more doubtful with northward extent from the boundary, which
may retreat somewhat northward into southeastern IA and toward the
WI/IL line later this afternoon, prior to frontal passage.
Probabilities mainly reflect the ongoing hazard, however, given
great uncertainties regarding airmass recovery behind it.

Farther southwest along/ahead of the front, widely scattered to
scattered afternoon thunderstorms are possible, offering damaging
gusts and large hail, as well as marginal tornado potential. A
substantial uncertainty regarding airmass recovery also is present
in this regime, because of trajectories emanating from a pronounced
theta-e deficit in AR and eastern OK produced by prior overnight
convection. A narrow corridor of sufficient boundary-layer moisture
to support 2500-3500 J/kg MLCAPE may develop just ahead of the
front. Some relative flow weaknesses progged in parts of the
mid/upper troposphere may render somewhat messy storm structures
after early supercell mode. Still, any storm(s) interacting with
the outflow boundary will have locally greater potential for
supercell longevity, and some risk for large to significant hail and
a tornado.

..Edwards/Goss.. 05/24/2024

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