202
FXUS63 KUNR 110822
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
222 AM MDT Sat Oct 11 2025

.KEY MESSAGES...

- Mild today with gusty southeasterly winds and small chances for
  precipitation
- Enhanced downslope winds for the eastern slopes of the Black
  Hills overnight tonight
- Upper level trough and cold front Sunday will bring very windy
  northwesterly winds, colder weather, and PoPs in the northwest
- Freezing temperatures possible Monday morning

&&

.DISCUSSION...(Today Through Friday)
Issued at 219 AM MDT Sat Oct 11 2025

08z surface analysis had high over the upper Midwest and lee
trough from central MT into eastern CO. Decent pressure gradient
between the two supporting gusty southeast winds at times where
40-50kt low-level jet (per KUDX WSR-88D VWP) is able to affect
the surface winds. Low-level jet supplying modest theta-e
advection over central SD ahead of a weak shortwave (noted on
water vapour loop over the central Plains). Result is some
sprinkles/spotty showers east of the Black Hills. Widening our
view, we see upper ridge to our east and upper low/trough over the
northwest CONUS. Distinct shortwave over the four corners area
heading out way for today.

Today/this evening, thermal ridge peaks over the CWA under
sustained southwesterly flow aloft. 700mb temperatures reach ~8C,
which supports highs in the 70s/lower 80s per guidance. Tight
pressure gradient continues with 30-40mph gusts (chance of >45mph
gusts per HREF <20%) east of the Black Hills likely into tonight.
Morning shortwave allows for lingering morning PoPs over central
SD. Four corners shortwave arrives this afternoon, whisked along
by 110kt upper level jet. Weak buoyancy/lift ahead of shortwave
brings low coverage shra/TS later this afternoon/evening.

Overnight/Sunday, main upper trough lifts through the Rockies
with distinct shortwave passing northwest of the CWA. Best QG-
forcing/moisture over MT/western WY, but enough moisture/lift for
some showers into Sunday over the northwest half of the CWA.
System will push initial cold front into the area late
tonight/early Sunday. Ahead of the front, eastern slopes of the
Black Hills may see enhanced downslope winds per 3-4mb pressure
difference/30-40kt boundary layer winds from about 06z-15z Sunday
(chance of >45mph gusts per HREF ~50%). Cold front will kill the
downslope enhancement Sunday morning, but 2-4mb/3hr pressure rises
behind it will stir up gusty westerly winds over the northwestern
SD plains in the morning. Then, as shortwave rapidly moves
northeast into Canada, a secondary cold front moves through with
moderate cold air advection and well-defined subsidence drying up
PoPs. 30-40kt 800mb winds/well-mixed boundary layer will lead to
very windy northwest winds in the afternoon/early evening.
Bufkit/MOS guidance portrays high-end Wind Advisory
event/possible low-end warning event. NBM/HREF probabilistic
guidance indicates chance of >55mph gusts <50%, so no headlines
yet. Low confidence temperature forecast given double cold frontal
passages.

Sunday night/Monday, high pressure moves into the CWA allowing
winds to drop, skies to clear, and frost/freezing temperatures to
develop. Headlines may be needed for areas that still have
susceptible vegetation.

Early next week, southwest flow aloft is expected. Seasonally
cool temperatures Monday moderate for the rest of the week. Weaker
shortwaves will pass earlier in the week, but it looks like a
better wave shows up for Thursday with the best PoPs/chance of
non-trivial QPF during the forecast period.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Saturday Night)
Issued At 1042 PM MDT Fri Oct 10 2025

VFR conditions will continue through the forecast period. South
to southeast breezy winds will continue through Saturday
afternoon. LLWS may develop east of the Black Hills tonight
through Saturday morning where the surface winds drop off.

&&

.FIRE WEATHER...
Issued At 219 AM MDT Sat Oct 11 2025

Gusty southeasterly winds today become very windy northwest
Sunday. Minimum relative humidities will dip into the 20s for
some, but should remain high enough to preclude Fire Weather
headlines.

&&

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

$$

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