132
ACUS01 KWNS 221254
SWODY1
SPC AC 221253

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0753 AM CDT Wed May 22 2024

Valid 221300Z - 231200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
CENTRAL TEXAS TO CENTRAL ARKANSAS...

...SUMMARY...
Within a long swath of severe-thunderstorm potential from central
Texas to the Lower Great Lakes, the greatest concentration of severe
weather (mainly large hail and damaging wind) should be across parts
of central Texas to central Arkansas.  A few tornadoes are also
possible.

...Synopsis...
An active mid/upper-level pattern persists southeast through
southwest of a longstanding cyclone over southern SK and paths of
southern MB.  That circulation will continue to meander erratically
near its present location through the period.  Meanwhile, a train of
shortwaves will cross the northwestern and central CONUS and Great
Lakes regions.  A strong shortwave trough -- with embedded 500-mb
low now over ON near the MN border -- should become stacked with its
deep surface cyclone this morning and drift erratically over ON
northwest of Lake Superior today.  The stacked low then should eject
toward James Bay tonight.

The associated cold front -- analyzed at 11Z from northern Lower MI
to southern IL, northwestern AR, southern OK, and northwest TX to
the Permian Basin -- should move by 00Z to near a line from
CLE-EVV-ARG-DUA-SJT-CNM.  The cold front should cross the lower
Great Lakes and much of NY through the end of the period, while
decelerating across parts of the lower/middle Ohio Valley.  The
western part of the front should become more diffuse and retreat
northward overnight across the southern Plains.  This will occur as
low-level mass response (including warm advection) intensifies,
ahead of a mid/upper cyclone moving eastward across the northwestern
CONUS toward the western WY/eastern ID region.  A dryline --
initially drawn over the Big Bend region south of the front --
should mix eastward to northern Coahuila and a frontal intersection
over west-central TX by mid/late afternoon.

...Southern Plains to Arklatex region...
A broken swath of elevated thunderstorms is ongoing over parts of
central OK to southeastern KS.  Isolated large hail is the main
concern, and should be for a few more hours.  Some of this activity
may aggregate into a broader belt or cluster of convection and shift
eastward to southeastward through the day, toward the front.

Additional thunderstorms should develop from midday through this
afternoon along/ahead of the front and mid/late afternoon near the
dryline, with the near-frontal activity having the longest and
strongest organizational potential.  A few supercells are expected
early in the convective cycle, and any supercell that stays
relatively discrete well into maturity will pose a risk of large to
giant hail.  Storm-scale/boundary processes also may locally boost
tornado potential.  Activity should grow upscale into the evening --
perhaps merging with remnants of earlier activity moving
southeastward from OK toward the surface front.  As this occurs, the
main threat will transition to damaging and severe gusts.  The
"enhanced" area represents the overlap of greatest hail and wind
probabilities with this transitional regime.

The warm sector southeast of the front, and east of the dryline,
will remain very moist -- characterized by upper 60s to mid 70s F
surface dew points.  Underlying steep midlevel lapse rates, and with
strong surface heating anticipated, the result should be a corridor
of 3000-4000 J/kg MLCAPE.  Given the strong heating and high ambient
theta-e, convective temperature may be attained even in the free
warm sector (away from the front and dryline), and despite the
prevalent EML.  Though forecast soundings show weaknesses in the
flow around 2-3 km, both low-level and deep-layer shear (effective-
shear magnitudes 55-65 kt) and lengthy hodographs will be present,
supporting potential for locally destructive hail.  Severe
downdrafts also are possible, both from individual supercells and
from convection resulting from aggregated cold pools.  The overall
threat should decrease with this activity as it shifts eastward-
southeastward toward south/east TX and over LA tonight.  However,
additional development atop the outflow may occur tonight farther
north near the Red River, helping to maintain some severe threat
(mainly in the form of hail and isolated severe gusts).

...Mid-South to Ohio Valley and lower Great Lakes...
Widely scattered to scattered thunderstorms, some in clusters, are
expected along this corridor from mid afternoon through the evening.
Damaging gusts will be the main concern, with isolated large hail
also possible. A marginal tornado threat also may develop,
particularly over portions of central/eastern OH to northwestern PA
and perhaps southwestern upstate NY, where low-level and deep shear
will be most favorable.

Once some ongoing clouds/precip over the Ohio Valley move away and
break up, surface heating should destabilize the boundary layer, in
concert with dewpoints commonly in the 60s F. This should yield a
prefrontal corridor of MLCAPE ranging from near 3000 J/kg over parts
of the Mid-South (where deep-layer lapse rates will be steepest) to
around 1500 J/kg over the area adjoining the lower Great Lakes.
35-45-kt effective-shear magnitudes will support a mix of multicell
and supercell modes, with upscale growth/clustering tending to limit
duration of supercells.

..Edwards/Goss.. 05/22/2024

$$