434
FXUS63 KUNR 302307
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
507 PM MDT Tue Sep 30 2025

.KEY MESSAGES...

- Much above normal temperatures expected Thursday and Friday

- Elevated fire weather conditions expected as well Thursday and Friday

- Significant pattern change in store beginning Friday night and
  continuing into next week

&&

.DISCUSSION...(This Evening Through Tuesday)
Issued at 136 PM MDT Tue Sep 30 2025

Latest water vapor imagery shows 500hpa ridge in place from the
Gulf to the Great Lakes region, with long wave troughing taking
place across the western CONUS. Embedded 500hpa waves are seen in
the SW flow aloft. One currently moving through eastern SD with
just a few high clouds associated. Another more robust wave
rotating out of NV and into UT. At the surface, weak low pressure
currently located across southeast MT with a surface trough
dropping south through northeast WY. Ahead of this trough, sfc
dwpts are in the low to mid 50s, while along and behind the
trough, sfc dwpts are in the low to mid 40s.

For tonight, aforementioned sfc trough will slide east as a weak
cool front, dropping temps slightly from those experienced today.
The cool down will be short lived through as 700hpa and 850hpa
thermal ridges rebound for Thursday. 850Hpa temps climb to +26C
across our southwestern and WY counties with 700hpa temps climbing
to +10C during the day on Friday. This could be when main fire
weather concerns arrive at 925hpa winds across southcentral SD
(Mellette/Todd/Tripp) counties climb into the 15-25kt
range...depending on your model of choice.

The pattern change will begin Friday night into Saturday as the
upper trough/closed low pushes into region, thus allowing a series
of cold fronts to move through the CWA through the weekend and
into next week. As disturbances slide into the region aiding in
forcing with decent moisture return ahead of the trof, appears
that weekend will be the best chance of seeing pcpn across the
area that we have had in awhile. The GFS is still hinting at the
possibility of a few flakes during the overnight hours across the
higher elevation of the Black Hills this weekend.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Wednesday Evening)
Issued At 505 PM MDT Tue Sep 30 2025

Gusty south-southwest winds will slowly diminish across the
western SD plains after 01z, but gusty winds will persist
overnight across NE WY. A cool front will move through the area
Wednesday morning turning the winds to the northwest during the
morning. VFR conditions are expected through the valid forecast
period.

&&

.FIRE WEATHER...
Issued At 136 PM MDT Tue Sep 30 2025

Much above normal temperatures are expected for Thursday and
Friday with readings from 15 to 25F above average. Minimum
relative humidities for both days, especially across the southwest
and south central parts of South Dakota will be at or around 20
percent. Wind speeds should be below the limits needed for Red
Flag criteria, however elevated fire weather conditions will be
present due to the high to very high grassland fire danger
indices. A cold front will move through the region Friday night
bringing in cooler air and increasing chances for precipitation
through the weekend into next week.

&&

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

$$

DISCUSSION/KEY MESSAGES...Hintz
AVIATION...SE
FIRE WEATHER...Hintz