507
FXUS63 KUNR 081146
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
546 AM MDT Tue Jul 8 2025

.KEY MESSAGES...

- Much warmer today with the possibility of a few storms over the
  Black Hills.

- Hotter on Wednesday with chances for storms (some potentially
  strong to severe) in the afternoon.

- Chances for storms continue Thursday and Friday

&&

.DISCUSSION...(Today Through Monday)
Issued at 310 AM MDT Tue Jul 8 2025

Current water vapor imagery and regional radar imagery shows an
MCS across IA/NE as the upper level shortwave moves off to the
east. Sfc high pressure is moving into the region as upper level
ridging builds over the western US. This is resulting in a dry and
mostly clear night for the CWA. Forecast soundings point at the
potential for some patchy fog to develop over southern SD this
morning, though confidence in coverage too low to put it in the
grids.

Upper ridge continues to build over the western US today as low
level thermal ridge builds into the Northern Plains. This will
support warmer conditions for Tuesday as highs climb into the
upper 80s to low 90s. Continued southerly flow and moisture
transport will lead to development of theta-e ridge over western
SD into northeastern WY. HREF grand ensemble paints 70-90+% probs
of 1000+J/kg CAPE along a corridor stretching from far
northeastern Crook County into the Black Hills and southwestern
SD. Height rises may limit convection across most of the region,
however terrain influenced convergence may be enough for a couple
of storms to develop over the Black Hills. Effective shear of
20-30kt may support organized convection with a marginal threat
for 1+" hail and strong winds. The ridge stays in place for
Wednesday with hotter conditions (highs in some spots could reach
the triple digits). Strong diurnal heating and sfc dewpoints in
the 50s to 60s will support moderate instability with areas on the
western SD plains seeing SBCAPE values of 1500+J/kg. A few subtle
disturbances riding the ridge may be enough to trigger at least
isolated convection across the western SD plains. Bulk shear will
be similar to Tuesday`s, which could support organized convection
and a marginal severe threat.

Potent lead shortwave and attendant cool front approaches the
region Thursday morning which could bring another round of storms
to the area. Marginal deep-layer shear and questions on timing of
the shortwave as well as how unstable the airmass will keep
confidence low for now. Trough will move through late Thursday
into Friday with increasing shear but greatly decreased CAPE.
Therefore, not anticipating much severe risk Thursday night into
Friday. CAA associated with an attendant cold front and pressure
rises behind said front may promote a breezy and mild Friday.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Wednesday Morning)
Issued At 542 AM MDT Tue Jul 8 2025

Mainly VFR conditions are expected through the TAF period. A storm
or two may develop over the Black Hills this afternoon with
associated LCL MVFR conditions.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

DISCUSSION/KEY MESSAGES...Wong
AVIATION...Wong