246
FXUS63 KUNR 292359
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
559 PM MDT Fri Aug 29 2025

.KEY MESSAGES...

- Chances for showers and thunderstorms through Sunday.

- Cool for the weekend, then warmer, more seasonable,
  temperatures early next week.

&&

.DISCUSSION...(This Evening Through Friday)
Issued at 210 PM MDT Fri Aug 29 2025

Water vapor imagery has an upper wave over northwestern South
Dakota with high pressure over the southern High Plains. At the
surface, a low is spinning over south central South Dakota, with
radar depicting showers and a few storms circulating around the
low. Temperatures at 20Z are mild, ranging from the 60s in the
Black Hills to the low 80s in parts of south central South
Dakota where it isn`t raining.

For tonight, mainly showers are expected behind the surface low, but
could see a few lightning strikes in the stronger cells.
Scattered storms are possible later this afternoon and evening
across south central South Dakota closer to the surface low where
MLCAPE is 500-1000 J/kg. However, shear is marginal, only 25-30
kts, so it will be difficult for storms to remain organized.
Overall, there is a potential for severe storms, but coverage
should be isolated and storms pulse up and down.

Scattered showers and storms will continue through Saturday as a
series of disturbances moves through the Northern Plains. PWAT
values of 1-1.5" (90th percentile - Max) will support heavy
rainfall in the stronger updrafts. HREF grand ensemble output
has 70-90+% probs of greater than 0.25" QPF over much of western
SD by 12z Sunday morning, with a less than 50% chance for greater
than 0.25" over northeastern Wyoming and Fall River County. There
are 50-70% chances for total precip to exceed 1", primarily over
the I-90 corridor east of Kadoka and into south central SD. Some
spot could see up to 1.5" or more where storms train, especially
in south central South Dakota.

Showers and storms end on Sunday as the upper ridge rebuilds over
the Rockies and drier northwest flow develops over the Northern
Plains. A cold front swings through the area Tuesday night,
bringing a chance for showers and storms along with cooler
temperatures for Wednesday. Right now, models indicate highs will
be 10-15F cooler on Wednesday than Tuesday.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Saturday Evening)
Issued At 547 PM MDT Fri Aug 29 2025

Shower coverage will be more sparse through the night before
increasing in coverage again during the day Saturday. Instability
will increase during peak heating, so included a PROB30 group at
each TAF site after 18Z/30. There is a signal for lower stratus
and possibly some patchy fog overnight into Saturday morning.
Generally expecting MVFR ceilings and visibilities; however, an
IFR ceiling can`t be ruled out by Saturday morning.

&&

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

$$

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