579
FXUS63 KUNR 270857
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
157 AM MST Thu Nov 27 2025

.KEY MESSAGES...

- Expect snow Friday/Saturday with mostly minor travel impacts
  per WSSI
- 10-20F below normal temperatures this weekend
- Additional snow may occur for the middle of next week

&&

.DISCUSSION...(Today Through Wednesday)
Issued at 153 AM MST Thu Nov 27 2025

08z surface analysis had weak ridge from central Canada into
eastern NE/KS. On the back side of the high, a stationary front
snakes from central MT into CO. Water vapour loop had northwest
flow over the northern Plains with next shortwave of interest
about ready to move into the northwest CONUS/southwest Canada.
Early morning weak shortwave associated with 140kt jet streak over
the CWA shaking out a few flurries per highway cameras/KUDX
WSR-88D radar returns. Main concern this forecast is impact of
upstream shortwave.

Today/tonight, northwest CONUS shortwave slips into the northern
Rockies. It will assist the development of weak low over central
MT which will transform stationary front into weak warm front,
slipping into the far southwest reaches of the CWA later tonight.
Weak lift along front will allow for thickening/lowering clouds
with low level southeasterly developing. Patchy light snow may
develop late. Temperatures will be near guidance.

Friday/Saturday, shortwave moves into the plains and then the
Midwest. MT surface low modestly strengthens as it moves southeast
along aforementioned surface boundary. 800-600mb frontogenesis
ahead of the surface low becomes increasingly well-defined as
modest QG-forcing ahead of shortwave moves through the CWA. Should
see a band of snow Friday morning shifting east of the CWA as it
intensifies, but weaker forcing will slip south over the CWA later
Friday into Saturday as boundary layer flow becomes northerly.
0-2km RH (>90%)/Froude numbers (>1) become favorable for some
upslope-ehnaced snow for the northern Black Hills Friday night
into Saturday. Latest probabilistic guidance suggests two areas of
concern for winter weather headlines. 1) Far northeast portions
of the CWA, including the Lemmon area where storm total snow
amounts may exceed 3". 2) The northern Black Hills where storm
total snow amounts may exceed 4". However, the 25-75th percentile
ranges are still quite large (1-6" for Bison for example), so will
not issue any headlines this morning given the uncertainty.
Northerly winds (15-25mph) behind surface low combined with
expected snowfall paint minor WSSI impacts, giving more credence
to taking a wait and see approach. Temperatures will be 10-20F
below normal.

Sunday through Thursday, northwest flow aloft continues with
splitting troughs. First batch largely misses the CWA
Sunday/Monday, but second batch may bring a shot of light snow for
the middle of next week per lift over low-level baroclinic zone
in place.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Thursday Night)
Issued At 1007 PM MST Wed Nov 26 2025

Sub 3kft AGL CIGS are impacting the KGCC terminal with MVFR
conditions. These MVFR conditions will last through 09z. At the
KRAP terminal CIGS are hovering between 3-4kft AGL with VFR
conditions prevailing across the terminal and should last through
the valid TAF period. Winds across both terminals will continue
to be light and variable through the overnight hours.

&&

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

$$

DISCUSSION/KEY MESSAGES...Helgeson
AVIATION...Woodward