220
ACUS01 KWNS 021247
SWODY1
SPC AC 021246

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0746 AM CDT Thu May 02 2024

Valid 021300Z - 031200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
NORTHWEST...NORTH-CENTRAL AND CENTRAL  TEXAS...

...SUMMARY...
Strong to severe thunderstorms will be possible today from parts of
the Upper Midwest to the southern Plains.  The greatest potential
appears to be over parts of northwest, north-central and central
Texas, where large to very large hail, severe gusts and a couple
tornadoes are possible.

...Synopsis...
In mid/upper levels, a complex cyclone -- now over southern SK and
eastern MT -- is forecast to move slowly and erratically eastward
stride the international border, orbited by several shortwaves/
vorticity lobes.  The most influential of those perturbations is
apparent in moisture-channel imagery over eastern WY to northwestern
CO.  This feature is forecast to strengthen and pivot to the
central/eastern Dakotas by 00Z, then across MN to northern WI and
western Lake Superior around 2Z tomorrow.  Meanwhile, broad west-
southwest to southwest flow in mid/upper levels -- with mainly
convectively augmented/modified embedded perturbations -- will cover
the central/southern Plains States.  MCVs are evident over western
IA, central OK and southeast TX.  These should move across the
Mississippi Valley this afternoon/evening, toward the Upper Great
Lakes, Ohio Valley and Tennessee Valley, respectively.

At the surface, 11Z analysis showed a low near STJ, with cold front
across northeastern to south-central KS, the northern/western TX
Panhandle, and north-central NM.  A dryline was drawn over the Llano
Estacado near the TX/NM line, southward into the western Big Bend
region.  By 00Z, the low should reach western WI, with cold front
over northern IL, central MO, southeastern KS, central/southwestern
OK, to a weak low over west-central TX.  The eastward-mixing dryline
will be overtaken by the cold front from north-south, with a 00Z
position from the southern low southward near DRT.  By 12Z, the cold
front should reach the northeastern IN/northwestern OH region,
extending southwestward to near a PAH-LIT-DAL line, then as a
stationary to warm front west-northwestward to central NM.

...Southern Plains to western Gulf Coast...
A large area of precip and embedded areas of thunderstorms is moving
eastward across eastern OK, northeast/east TX, and western LA,
anchored by some strong thunderstorm clusters in the southeast
TX/southwestern LA area.  Isolated, marginally severe hail and/or
gusts may occur for a few more hours.

Behind that activity, an outflow boundary extends across south-
central TX, the Hill Country and Concho Valley regions, to the
Permian Basin.  Northward-directed warm/moist advection and theta-e
recovery will occur today over west-central/northwest TX east of the
dryline, before being intercepted by the cold front over the
northwest TX/southwestern OK region this afternoon.  Farther
northeast over most of OK, severe potential will be more isolated
and conditional near the front, given the presence of partially
modified MCS-outflow air instead of a relatively undisturbed Gulf
boundary layer.

Isolated to scattered thunderstorms are expected to develop near the
dryline and along the front this afternoon, with the most favorable
parameter space, greatest low-level convergence, and densest
convective concentration for severe potential being in and near the
"slight" area.  The northern rim of the residual outflow boundary
will diffuse and move into this region as well, providing a
potential low-level vorticity source that may help to offset some
flow weaknesses aloft in terms of supporting supercell organization.
30-40 kt effective-shear magnitudes are possible. Forecast soundings
reasonably indicate modest low-level flow supporting nearly straight
hodographs with both left- and right-moving cells possible.  Strong
lapse rates -- generally 7.5 to 8 deg C from surface through 400 mb
-- and mid/upper 60s F dewpoints, will support a plume of 3000-4500
J/kg MLCAPE over much of northwest, west-central and south-central/
southwest TX ahead of the dryline.  Large to very large hail is the
greatest concern, though storm-scale processes and boundary
interactions may favor a tornado threat as well.  Upscale
aggregation of some of this convection is possible, increasing the
severe-gust potential for at least a few hours into this evening and
tonight.

...Midwest...
A band of initial convection is crossing portions of IA and
northwestern MO, ahead of the surface cold front.  As this activity
moves eastward into weakly destabilizing parts of IL/WI/northern MO
through the day, some intensification may occur, resulting in
isolated damaging gusts and marginally severe hail from the
strongest segments.  Behind this activity and along/ahead of the
cold front, modest destabilization (from warm advection and limited
insolation) will occur, supporting isolated to widely scattered
afternoon thunderstorm development along the front, and additional
risk of gusts/hail near severe limits.  Favorable deep shear
(effective-shear magnitudes around 40-50 kt) will spread over the
area.  However, limited instability is expected, with modest deep-
layer lapse rates and trajectories from convectively processed
source regions, keeping MLCAPE generally in the 500-1000 J/kg range
in a narrow prefrontal corridor.  Activity should weaken in the
evening as it moves into a more-stable airmass.

..Edwards/Leitman.. 05/02/2024

$$