ACUS01 KWNS 191255
SWODY1
SPC AC 191253

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0753 AM CDT Fri Jul 19 2024

Valid 191300Z - 201200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF SOUTHWESTERN/SOUTH-CENTRAL NEBRASKA ACROSS WESTERN KANSAS AND
EXTREME EASTERN COLORADO...

...SUMMARY...
The most favorable corridor for damaging thunderstorm gusts (some
potentially exceeding 70 mph) will be late this afternoon and
evening from parts of southwestern/south-central Nebraska across
western Kansas and extreme eastern Colorado.

...Synopsis...
A large anticyclone in mid/upper levels -- initially centered over north-central/northeastern AZ -- is forecast to retrograde
northwestward over more of the Great Basin today. This will result
in northwesterly flow over the northern Great Plains, and
substantially northerly mid/upper flow over most of the rest of the
Plains States, in conjunction with the persistent eastern CONUS
longwave trough. Within that regime, a shortwave trough now located
over eastern MT is expected to move southeastward to southern SD and
northern NE by 00Z. Overnight, this feature may phase with another,
weaker trough to its east, as well as take on convectively generated
vorticity, and move over eastern NE/IA and vicinity.

At the surface, a weak, slow-moving frontal zone (cold or warm on
various mesoscale segments) was analyzed at 11Z from the Hampton
Roads area across northern parts of GA/AL/MS/LA, becoming diffuse
over central/north TX. Richest maritime/tropical moisture was (and
will remain) confined along and south of that boundary through the
period. However, a corridor of relatively maximized moisture, with
dewpoints upper 50s to low 60s F -- was analyzed from the central
Dakotas to western/central NE and western KS, with some eastward shifting/erosion possible on the west side today as heating/mixing
occur. A lee trough should remain over the High Plains from eastern
MT to the western NE Panhandle and eastern CO, to eastern NM. A
trough now over parts of central SD into northwestern NE, to a low
at the intersection of the troughs near BFF, potentially will become
better defined and shifting southeast amid mass response to the
approaching perturbation aloft.

...Central/southern Great Plains...
Isolated to scattered thunderstorms are expected to develop this
afternoon over both the Front Range/Foothills corridor of CO and
southeastern WY, and near a surface trough across northern/central
NE. Damaging gusts and large hail will be possible with early-stage
activity over NE, with gusts the more probable hazard in the CO
convection. Activity should evolve upscale in both areas, moving
southeastward over CO and generally southward with some westward
backbuilding over central NE to western KS. An MCS with organizing
cold pool appears increasingly probable, with one or more associated
swaths of severe gusts expected.

The best-organized and most-intense severe-wind potential may begin
sooner and farther north, and conditionally may persist farther
south before overnight weakening, than depicted in the "enhanced"/
30%-wind area. However, a preponderance of guidance -- reasonably,
given the overall pattern and placement of the moisture/instability
corridor -- has settled on the area from southwestern NE southward
across western KS to near the OK Panhandle as a most-probable
corridor for severe gusts. At least isolated significant-severe
(65+ kt) gusts also may be observed.

Enough vertical shear will be present to support supercell potential
with any relatively discrete convection in the early stages, as
strong veering with height contributes to 30-45-kt effective-shear
magnitudes, despite lacking stronger midlevel winds. Activity over
CO will be in weaker (but still sufficient) low-level moisture and higher-based. However, even near the moist axis over central NE and
western KS, a deeply well-mixed boundary layer will support wind
potential. Strong surface heating should help to boost MLCAPE to
2000-2500 J/kg over much of central/west-central NE, and 1500-2000
J/kg over western KS. Activity moving into eastern NE into central
KS will encounter weaker instability and greater CINH, limiting
eastward extent of the severe threat, while nocturnal cooling and
related stabilization will decrease the threat southward into
northwestern OK and the Panhandles. How far the severe-gust threat
penetrates into that stabilizing air will depend largely on strength
of cold-pool-driven forced ascent and associated downdraft
production, driven by low-predictability internal dynamics of the
complex.

..Edwards/Broyles.. 07/19/2024

$$
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