100
FXUS63 KUNR 152313
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
413 PM MST Mon Dec 15 2025

.KEY MESSAGES...

- Mild and dry through Wednesday morning
- Two cold fronts later Wednesday may bring wind gusts in excess
  of 60mph into Thursday morning
- Elevated fire weather concerns through Wednesday for snowless
  areas
- Cooler Thursday, warmer Friday, then somewhat above normal for
  the weekend into early next week

&&

.DISCUSSION...(This Evening Through Monday)
Issued at 1248 PM MST Mon Dec 15 2025

19z surface analysis depicted low pressure over central BC with
warm front into the upper Midwest. Diffuse high over the CWA with
cirrus-filtered sunshine/mild temperatures. Water vapour loop had
jet zipping over the US/Canadian border. Embedded waves will
bring our sensible weather for the period.

Tonight/Tuesday, BC low moves south/southeast as embedded
shortwave moves across southern Canada. It will drag a glancing
cool front into the CWA later tonight. Breezy/windy spots behind
it Tuesday, particularly across northwestern SD where the
probability of >45mph wind gusts is less than 50% (due to the
uncertainty of how well-mixed the boundary layer will be).
Temperatures will be mild with readings 10-20F above normal.

Wednesday into Thursday, better-defined shortwave races through
the northern Rockies into the northern Plains. Deepening surface
low develops to the lee of the Rockies, moving into the the upper
Midwest. The first cold front moves through late Wednesday with
3-6mb/3hr pressure rises and modest cold air advection. Forecast
soundings suggest headlineable gusty west/northwest winds will
occur, but the main story may be the second cold front very early
Thursday morning. Strong cold air advection paints 6-12mb/3hr
pressure rises behind the cold front with a northwest 40-70kt+ low
level wind core for the western SD plains. Some question as to
how much will make it to the surface, which is reflected in
probabilistic guidance, but Bufkit/MOS guidance strength is
robust. NBM has 50% chance >60mph gusts and 20% chance >70mph
gusts. ECMWF EFI depicts 80-100 percentile wind gusts for the
event with 0-2 shift of tails. If wind potential is maximized, we
may see damage from this wind event. Moisture ahead of system will
bring mostly rain to the area before the colder air arrives with
strong subsidence/drying. Highs Thursday will be much colder.

Looking ahead, a strong warmup Friday is replaced by "regular"
somewhat above normal temperatures and chances for some light
precipitation from time-to-time as westerly flow aloft trends
southwesterly toward the end of the forecast.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Tuesday Evening)
Issued At 413 PM MST Mon Dec 15 2025

VFR conditions will continue through the TAF period. Breezy
northwest winds are expected across the western SD plains in the
afternoon, with gusts to 35 kt.

&&

.FIRE WEATHER...
Issued At 1248 PM MST Mon Dec 15 2025

Temperatures 10-20F above normal combined with breezy/gusty winds
at times will cause elevated fire weather concerns through
Wednesday for areas where snow cover is gone.

&&

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

$$

DISCUSSION/KEY MESSAGES...Helgeson
AVIATION...13
FIRE WEATHER...Helgeson