983
FXUS63 KUNR 162338
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
438 PM MST Tue Dec 16 2025

.KEY MESSAGES...

- Damaging winds possible Wednesday into Thursday morning with
  gusts from 60-75mph
- Limited snow squall potential Wednesday night, but some blowing
  snow may occur where it snows
- Near critical fire weather conditions Wednesday

&&

.DISCUSSION...(This Evening Through Tuesday)
Issued at 215 PM MST Tue Dec 16 2025

21z surface analysis had surface low over ON with trailing
dissipating cool front into eastern WY. Gusty winds behind front
subsiding this afternoon per decreasing pressure rises and
eventual decoupling of the boundary layer. Water vapour loop had
shortwave trough from south-central Canada into WY. Bit of ACCAS
over south-central SD earlier had dissipated with leftover weak
radar returns and a few more over southeast MT. Looking upstream,
next shortwave wrapping up west of BC. Feature will bring high
impact weather Wednesday into Thursday morning.

Tonight through Thursday afternoon, BC shortwave becomes strong
fast-moving compact upper low as it races through ND on it`s way
to the Midwest. Anomalously deep surface low develops over the
lee of the Rockies, moving into the Great Lakes. It will drag two
cold fronts through the CWA with the first Wednesday afternoon and
the strongest overnight Wednesday. Ahead of the cold front
Wednesday, deeply mixed boundary layer will support gusty
west/southwest winds over parts of the CWA, but especially from
southern Campbell to Fall River County and then another area
northeast of the Black Hills. First cold front brings 4-8mb/3hr
pressure rises/round #1 of high winds late Wednesday
afternoon/evening. Round #2 drops in overnight Wednesday with
6-11mb/3hr pressure rises behind the secondary cold front
supported by sharp cold air advection/strong subsidence. Forecast
soundings depict impressive wind from the Black Hills to the
adjacent plains with 70-90kt core around 800-700mb. Bufkit
momentum transfer projections for KRAP show boundary layer mean
mixed wind around 50kts with 70-80kts at the top. For much of the
CWA, HREF guidance for Wednesday into Thursday morning gives >60%
chance >60mph gusts with a corridor of a 60-80% chance >70 mph
wind gusts just east of the Black Hills. ECMWF EFI just as lit up
with 80-100th percentile wind gust potential and shift of tails
from 1-2. Shaping up to be a high end wind event with power
outages, tree damage, and other assorted high wind impacts we
don`t normally get with "regular" high wind events. 80mph wind
gusts possible. Highlights issued to account. Most of the
moisture associated with this system passes through Wednesday
afternoon/early evening when wet bulb zero heights portray rain.
Some snow expected with the second cold front which may cause
transient visibility restrictions. NAM snow squall parameter has
the best chance over northwestern SD with the second cold front
Wednesday night. Some upslope may occur over the northern Black
Hills with a couple of inches of snow accumulation resulting in
some blowing snow. May have to take a look a closer look at winter
headlines on later shifts for the northern Black Hills. Given
anomalously warm antecedent weather, blowable snow on the plains
should be zero. Temperatures will be near guidance and much colder
for Thursday.

Westerly upper level flow Friday slowly becomes southwesterly by the
middle of next week. A series of moisture-starved disturbances will
pass by with much warmer temperatures for Friday, then colder for
the weekend, and then warmer next week. Strap in for the ride.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Wednesday Evening)
Issued At 434 PM MST Tue Dec 16 2025

VFR conditions will continue through the TAF period through
Wednesday morning.

Strong southwesterly winds will develop across NE WY after 12z
Wednesday. Gusts up to 35-40 knots will be possible, especially
across NE WY. Then a vigorous cold front will cross the region
Wednesday afternoon/evening, bringing very strong winds, with
gusts to 60kt or even higher in some locations. A band of rain
cross the area Wednesday afternoon, changing to snow as the front
passes. This could result in locally MVFR/IFR visibility and
ceilings.

&&

.FIRE WEATHER...
Issued At 215 PM MST Tue Dec 16 2025

Near critical fire weather conditions are expected Wednesday due
to unseasonably warm weather and strong, gusty winds. Minimum
relative humidities will only drop to 30-50%, which will preclude
headlines.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...High Wind Warning from noon Wednesday to 11 AM MST Thursday for
     SDZ001-002-012-013-025-072-073-078.
     High Wind Warning from midnight MST /1 AM CST/ Wednesday night
     to 1 PM MST /2 PM CST/ Thursday for SDZ014-032-043-044-046-
     047-049-077.
     High Wind Warning from 2 PM Wednesday to 8 AM MST Thursday for
     SDZ024-027>029.
     High Wind Warning from 10 PM Wednesday to 1 PM MST Thursday for
     SDZ026-030-031-042-074>076.
     High Wind Warning from 11 AM to 5 PM MST Wednesday for SDZ041.
WY...High Wind Warning from noon Wednesday to 11 AM MST Thursday for
     WYZ060.
     High Wind Warning from 2 PM Wednesday to 8 AM MST Thursday for
     WYZ057.
     High Wind Warning from 11 AM to 5 PM MST Wednesday for WYZ059.
     High Wind Warning from 8 PM Wednesday to 8 AM MST Thursday for
     WYZ054-056.
     High Wind Warning from 5 AM to 5 PM MST Wednesday for WYZ055-058.
&&

$$

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