FXUS63 KUNR 120234

AFDUNR



Area Forecast Discussion For Western SD and Northeastern WY

National Weather Service Rapid City SD

734 PM MST Thu Dec 11 2025



.KEY MESSAGES...



-Strong cold front will shift into the region tonight with some 

 light snow expected, mainly across the western third



-Cold and snowy Friday into Sat with snow accums expected, 

 heaviest across NW SD Friday night



-Warm and dry the first half of next week



&&



.UPDATE...

Issued at 727 PM MST Thu Dec 11 2025



02z surface analysis showed first cold front from central NE into

central WY and secondary (much colder) front has passed through

Miles City and Baker, MT. 3-6mb/3hr pressure rises behind second 

front should accelerate it southward overnight as well as bring a

short increase in gusty wind with it's passage. With onset of 

nighttime cooling, T/Td spreads behind first cold front have 

collided to produce patchy/areas of fog over much of the CWA, but 

especially from the north/east slopes of the Black Hills 

(north/northeast boundary layer flow) into south-central SD. 

Streaks of light precipitation (mostly rain down low) under 150kt 

jet streak continue along low level baroclinic zone in place.



Forecast has been adjusted to paint patchy/areas of fog into the

night, adjust the changeover to snow a bit, and to increase pops 

where low level frontogenesis most focused.



&&



.DISCUSSION...(This Evening Through Thursday)

Issued at 113 PM MST Thu Dec 11 2025



Active northern stream will continue to bring large swings in 

temps along with precip chances through the end of the week. 

Massive western CONUS ridge has directed another clipper system 

along the top of the ridge. First cold front has settled south 

into western SD with mainly 30s behind it and 50s-60s ahead to 

the south. Lingering WAA precip cross NW SD is expected to taper 

off this afternoon. CAA will ramp up overnight as NW winds 

increase and the secondary arctic front drops into the region. 

Some light precip will develop over the western third this 

evening. Precip may start as rain first then quickly switch to 

snow. An inch or 2 of accums will be possible across northeast WY 

and the northern Black Hills. Baroclinic zone will then stall 

over the region with several weak impulses agitating the flow and

supporting rounds of light snow. Accums will range form 1 to 2 

inches in the SW half to third with 3 to 6 inches across the NE 

half, heaviest across far NW SD. This prolonged period of FGEN is 

expected to ensue sometime Friday morning and spread southeast 

over the region, intensifying Friday night when the strong lift is

expected. Will defer headlines to the mid shift to allow fine 

tuning of timing and amounts. In addition, some upslope fog will 

also be possible later Friday into Sat. Expect much colder temps 

with readings below zero across NW SD Sat morning and Sunday 

morning, supporting wind chills 15 to 25 below there. The cold 

spell will be short lived though. Upper ridge begins to shift east

Sunday with things quickly warming back up next week, along with 

breezy conds as the nearby active northern stream supports 

traversing impulses. The warm up will be quite strong Sun with 

northeast WY and the higher elevations of the Black Hills expected

to see highs back in the 50s. The warm air will spread east on 

the Plains Sunday, but will hinge on the strength of the wind, 

with stronger wind allowing for better mixing and warmer temps. 

Expect warm and dry conds into Wed at which time a stronger 

clipper system will support a cold front into the region along 

with chances for rain and snow.



&&



.AVIATION...(For the 00Z TAFS Through 00Z Friday Evening)

Issued At 429 PM MST Thu Dec 11 2025



A secondary cold front will move through the area tonight bringing

widespread MVFR/IFR conditions, which will persist through Friday.

Mixed ra/sn will become all snow overnight with the highest

probabilities of snowfall over northeastern WY/Black Hills 

tonight and then over the entire area Friday. LIFR conditions will

occur over the Black Hills later tonight into Friday as snow 

intensity rises.



&&



.UNR WATCHES/WARNINGS/ADVISORIES...

SD...None.

WY...None.

&&



$$



UPDATE...Helgeson

DISCUSSION/KEY MESSAGES...JC

AVIATION...Helgeson