299
ACUS01 KWNS 040604
SWODY1
SPC AC 040602

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0102 AM CDT Mon Aug 04 2025

Valid 041200Z - 051200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
FAR EASTERN WYOMING...SOUTHWEST SOUTH DAKOTA...WESTERN NEBRASKA AND
NORTHEAST COLORADO/KANSAS...

...SUMMARY...
Thunderstorms with severe gusts and hail will be possible today and
tonight from parts of the northern Rockies into the Dakotas and
central/southern High Plains.

..Central High Plains...
Rather pronounced shortwave ridging is expected across the central
High Plains through much of the day as troughing intensifies over
the Northwest. With building heights aloft, synoptic forcing for
ascent appears weak. Still, a subtle embedded perturbation should
move eastward across the Rockies late in the afternoon, but it is
unclear how much ascent this feature will support. Given the lack of
stronger forcing for ascent, convective development over the central
High Plains appears tied to diurnal heating and weak low-level
upslope flow along the higher terrain of the Black Hills and eastern
WY. This should favor widely scattered storm development within a
hot and unstable air mass (MLCAPE 2500-3000 J/kg). Northwesterly
flow aloft with elongated hodographs and 45-55 kt of effective shear
will favor high-based supercells initially capable of hail (some
significant) and damaging gusts before moving into more substantial
low-level moisture farther east.

With time, upscale growth appears likely given the strong outflow
expected from the drier low-levels. Most CAM guidance shows one or
more clusters evolving across western/central NE and northeast CO
this evening. Aided by a 40+ kt low-level jet, continued upscale
growth should support these clusters of strong to severe storms into
the overnight hours where damaging winds will be possible.

...Southeast CO into the OK/TX Panhandles...
Strong heating along a lee trough could support isolated
thunderstorm development across the Raton Mesa and TX/OK Panhandles
late this afternoon/evening. Large-scale forcing is not particularly
strong beneath the building upper ridge. Still, model soundings show
uncapped profiles with large buoyancy (3000+ J/kg MLCAPE) and 40-50
kt of effective shear. Should a storm develop it would likely be
supercellular with the potential for hail and damaging gusts. A
brief tornado is also possible as the low-level jet helps expand
hodographs near sunset. The primary uncertainty for higher severe
probabilities remains the limited forcing for ascent and the
uncertainty on higher storm coverage.

...Montana...
Model guidance shows a negatively tilted shortwave trough and
mid-level jet streak moving across portions of the Northwest.  This
feature will track northeastward today, spreading broad ascent
across the Northern Rockies. Steep low and mid-level lapse rates
atop modest surface moisture (40s and 50s F dewpoints) will result
in sufficient SBCAPE for scattered thunderstorm development over the
mountains of central ID and western MT by mid-afternoon.  Convection
will become more numerous and spread into central and eventually
eastern MT through the evening.  Elongated hodographs (30-40 kt of
bulk shear) will support a few organized clusters and rotating
storms capable of damaging winds from strong downdrafts and some
hail. The primary uncertainty for higher severe probabilities is the
potential for limited buoyancy and lack of a stronger signal for
consolidating outflow favoring higher damaging wind potential.

..Lyons.. 08/04/2025

$$