660
FXUS63 KUNR 221126
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
526 AM MDT Fri Aug 22 2025

.KEY MESSAGES...

- Chances of showers and thunderstorms through tonight.

- Mild and mostly dry conditions this weekend through much of next
  week.

&&

.DISCUSSION...(Today Through Thursday)
Issued at 221 AM MDT Fri Aug 22 2025

Latest water vapor imagery shows an upper low centered over the
Saskatchewan/Manitoba border with the upper trof extending
through eastern Montana and a vort max moving through northwestern
South Dakota. Additionally, a large area of high pressure is
centered over the Southern Rockies, creating zonal flow across the
forecast area. Upper level analysis shows divergence at 300 mb
with a slight 500 mb height perturbation over northwestern South
Dakota. At the surface, the frontal boundary extends from eastern
South Dakota, through south central South Dakota into western
Nebraska/southeastern Wyoming and then up through central Wyoming
into western Montana. Latest radar imagery is showing scattered
showers and thunderstorms ongoing across northwestern South
Dakota correlating to the vort max and the upper level divergence
and in central South Dakota near the front.

For today, the upper trof will continue to push east and the front
will continue to sink southward. Though the upper jet will sink
southward, the core of the streak will shift eastward away from the
region, which will bring increased forcing for ascent but decreasing
deep-layer bulk shear magnitudes. Altogether, this should lead to
continued shower/storm activity--especially closer to the baroclinic
zone--but it will also reduce the potential for strong/severe storms.

Showers and storms will end tonight, as the upper trof shifts east
of the area. High pressure over the southern Rockies will continue
to build, putting the area into a northwest flow pattern. Ensemble
model consensus indicates northwest flow will continue for much of
the upcoming week. As is the norm for northwest flow, we could see
some energy push through at times, creating a chance for an isolated
shower or storm. However, moisture will be limited as the air dries
out coming over the Rockies. 850 temps look to remain below normal
through Tuesday, before rising slightly to near normal for Wednesday
through Friday next week.  As such, a mild and mostly dry period is
likely from Saturday through much of next week.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Saturday Morning)
Issued At 507 AM MDT Fri Aug 22 2025

Scattered showers and thunderstorms will continue this morning,
becoming isolated by midday. Additional storms will develop this
afternoon and evening across southwestern South Dakota and should
continue overnight.

&&

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

$$

DISCUSSION/KEY MESSAGES...Smith
AVIATION...Smith