502
FXUS63 KUNR 172354
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
554 PM MDT Thu Sep 17 2026

.KEY MESSAGES...

- Cooler and wet conditions will persist through the weekend.

- Gradual warmup early next week.

&&

.DISCUSSION...(This Evening Through Thursday)
Issued at 110 PM MDT Thu Sep 17 2026

Water Vapor and upper air models show southwest flow aloft, as
ridging sits over the northern and central plains. Upper low
currently sits over the west coast, while a shortwave currently
sits over WY riding the southwest flow into the Dakotas. 18Z
surface analysis shows associated surface low over the CO/WY
border. Winds are currently out of the southeast, with temps
ranging from around 60 to mid 70s this afternoon. Radar currently
has patchy precipitation over the southern half of the CWA as the
disturbance moves into the region.

Shortwave will continue to lift into the Dakotas today, bringing
widespread precipitation with it. HREF 24 hour probabilities for
0.5" or more QPF show the highest chances (60-95%) over south-
central SD. Much of the area could at least see wetting rain
through Friday morning. Some areas could see some lightning at
times with this precipitation, however severe storms are not
anticipated.

Friday will be mostly dry as the shortwave exits the area early
morning. Shortwave ridging sets up over the northern plains, but
by Saturday the aformentioned upper low shifts over the Rockies
bringing cooler temperatures and more potential for widespread
precipitation Saturday and Sunday. A bit more uncertainty with
QPF, as much will depend on the track of the low as it moves into
the northern/central plains, but currently the wettest day looks
to be Sunday. Decent chance that some areas will see more wetting
rains, with potential for much of the area to see upwards of a
half inch Sunday into Monday morning.

By the latter half of monday, upper ridge builds over the plains,
bringing a warming trend Monday through much of next week.
Temperatures climb back to at or above normal by Tuesday and
Wednesday.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Friday Evening)
Issued At 546 PM MDT Thu Sep 17 2026

Widespread rain showers with isolated thunderstorms will continue
to move through the area this evening with MVFR/IFR conditions in
heavier showers. Rain showers and thunderstorms will begin to
exit the region to the east around 09-12z Friday morning. Low
clouds and fog are expected overnight Thursday into Friday
morning with IFR/LIFR conditions at KRAP. Low confidence on the
fog and low clouds impacting KGCC so removed the lower aviation
conditions. Will reassess later and update if needed.

&&

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

$$

DISCUSSION...Dye
AVIATION...GS