782
ACUS01 KWNS 041253
SWODY1
SPC AC 041251

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0751 AM CDT Sat May 04 2024

Valid 041300Z - 051200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PORTIONS
OF WEST TEXAS AND EXTREME SOUTHEASTERN NEW MEXICO...

...SUMMARY...
Scattered severe thunderstorms are expected across parts of the
southern High Plains into the Hill Country of central Texas this
afternoon and evening. Several storms may produce very large hail,
and a couple strong tornadoes are possible.

...Synopsis...
Starting today and for several more, the greatest mid upper-level
influence on severe-thunderstorm potential will be related to a
well-developed cyclone now centered over the northeastern Pacific,
about 250 nm west of ONP.  The associated 500-mb low should dig
southeastward to northeastern CA by the end of the period (12Z
tomorrow), with a large swath of preceding difluent flow spreading
over the Rocky Mountain States.  In response to these developments,
a southern-stream perturbation -- evident in moisture-channel
imagery from parts of AZ across northern/central Baja -- will pivot
east-northeastward.  This feature should reach southern NM and
Chihuahua by 00Z, then merge with convectively generated vorticity
over west TX this evening.  The perturbation then should reach
western OK and north-central to south-central TX by 12Z.

At the surface, 11Z analysis showed an elongated area of low
pressure over southwestern to north-central IA, with cold front
southwestward across southeastern KS, southwestern OK, and the Llano
Estacado between PVW-CVS.  A warm front was analyzed from
southeastern IA across northeastern MO and southern IL.  As the
low-pressure area migrates toward Lake Michigan by 00Z, the cold
front is forecast to reach northeastern to extreme southern IL, the
central Ozarks, southern OK, and west-central TX, becoming muddled
by convective processes southwestward through the Permian Basin/
lower Pecos Valley region.  By 12Z, the low should reach eastern
Lower MI, with cold front over IN, central AR, and northeast TX,
becoming ill-defined amid expansive outflow southwestward from there
in TX.  The warm front should reach eastern IL, central IN and
northwestern OH by 00Z.

...TX/southern OK/extreme southeastern NM...
Widely scattered to scattered thunderstorms are expected to form
this afternoon along and behind the cold front over west TX and
southeastern NM, as well as ahead of the cold front, near the
dryline and over strongly heated, relatively high elevations west of
the Pecos Valley.  Large hail will be a threat on both sides of the
front, with severe-wind and tornado potential more prevalent to its
south.  One or two dominant, prefrontal, mid/late-afternoon
supercells may evolve and remain south of the front -- through the
lower Pecos Valley/FST region -- to sustain threats for strong
tornadoes and very large/destructive hail.  As in the last few days,
storm-boundary and storm-storm interactions may factor importantly
into localized enhancement of tornado risk.

Strong heating and moist advection are expected this afternoon south
of the front, increasing theta-e and reducing MLCINH in support of
initiation.  70s F surface dewpoints are already present not far
upstream in the Rio Grande Valley and below the Balcones Escarpment,
around DRT-UVA.  Mid 60s to near 70 F dewpoints and 1-1.5-inch PW
should be common east of the dryline, and between the front and the
Rio Grande, by late afternoon, supporting MLCAPE of 2500-3500 J/kg
amid steep low/middle-level lapse rates.  Kinematically, by 00Z,
this area will be in a vertical superposition of:
1.  The supportive large-scale ascent regime of the left-exit region
of a broad subtropical jet, whose axis remains over northern MX.
2.  A strengthening, southeasterly LLJ, lengthening/enlarging the
hodograph.  This LLJ also should transport rich low-level moisture
into convection over the region, while providing strong
storm-relative low-level winds.
3.  Strengthening flow near 500 mb, supporting increases in
effective-shear magnitudes to around 45-60 kt.

Upscale merger/growth of convection is expected this evening, with
resulting MCS shifting eastward over the Edwards Plateau/Hill
Country before weakening late tonight.  Damaging to severe gusts
will become the main threat, though embedded tornadic circulations
and isolated large hail will remain possible.  The northern part of
this activity also may grow/merge with initially separate, less-
organized (but still potentially marginally severe) convection in
the Red River region of southern OK and north TX.

...North/northeast TX to mid Mississippi Valley vicinity...
Isolated to scattered thunderstorms -- some in lines and
multicellular clusters -- should affect portions of this broad
corridor today into this evening along and ahead of the surface cold
front.  Isolated damaging to severe gusts and large hail are the
main concerns.  Due to limited low/middle-level lapse rates,
adequate but not rich moisture, and modest vertical shear, severe
potential in this swath should be less focused, and more marginal in
magnitude than over the "slight" and "enhanced" areas.

..Edwards/Broyles.. 05/04/2024

$$