439
FXUS63 KUNR 090505
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1005 PM MST Mon Dec 8 2025

.KEY MESSAGES...

- Mild, dry and breezy this afternoon. Wind gusts occasionally up
  to 45 mph possible

- Strong winds likely Tuesday. A High Wind Warning is now in
  effect for most of western SD

- Turning colder with chances for light snow across the region
  Wednesday through Friday

&&

.UPDATE...
Issued at 803 PM MST Mon Dec 8 2025

Have upped wind speeds over northeastern WY per latest
deterministic guidance in combination with earlier probabilistic
guidance. 00z NAM Bufkit soundings/HRRR suggest high wind warning
winds over northeastern WY Tuesday, but MOS not as excited with
best isallobaric forcing (4-5mb/3hr pressure rises) over western
SD. NBM depicts <20% chance of >=58mph gusts for northeastern WY.
Western SD plains have the expected high probabilities. Thus, the
current wind headlines look good. Midnight shift can take one
more look before strong cold front arrives.

&&

.DISCUSSION...(This Evening Through Monday)
Issued at 1247 PM MST Mon Dec 8 2025

Rest of today...Not much going on across the region this
afternoon. A weak wave is passing through which has kicked up the
winds a bit over the last hour. These breezy conditions will
continue for several more hours before they diminish. Winds could
occasionally gust up to 45 mph with mild temperatures.

Heading into Tuesday morning a stronger area of low pressure will
bring a surface front through the region during the early morning
hours and ahead of the main wind event. This will provide a window
for some light snow or a rain/snow mix to occur across the
northwestern portions of the area. Expecting a quick transition to
all rain as the strong downsloping winds develop which will
quickly warm temperatures. This area of low pressure will slide to
the SE across central ND and SD Tuesday. A belt of 55-60 not winds
will overspread the region quickly and winds are expected to turn
gusty rather quickly during the morning hours on Tuesday. a suite
of HI-RES models have come in a bit stronger with these winds
aloft around the 850mb level showing a concentrated area of 70+
knot winds across the eastern plains. While these winds aloft are
impressive the strong CAA advection we were expecting has not been
pushed off to the north and east and this will limit some mixing
down of these winds. But precipitation post frontal boundary will
linger across the region in the form of banded lines of rain
showers. These will be a concern as locations under these areas of
precipitation may see sudden bursts of rain/snow, snow or, graupel
as well as strong wind gusts as those strong winds aloft will mix
down with the precipitation. Outside of that, much of western SD
and the eastern Plains will experience strong winds throughout
much of the day on Tuesday with wind gusts commonly exceeding 60
mph with a few locations seeing wind gusts at or over 65 mph.
Given this a High Wind Warning is now in affect for Tuesday
morning through late Tuesday night.

Another system is on the heels with the exiting system with
unsettled weather expected to persist Wednesday through the rest
of the week. Models are beginning to settle in on the overall long
wave pattern but the mesoscale parameters that will determine how
quickly we transition to all snow, how strong the CAA will be and
surface flow still need to be ironed out to pinpoint just how much
snow will fall and where the heaviest snow will occur. The
overall consensus at this time is for widespread snow looks
likely with light accumulations possible. With this pattern shift
temperatures are also expected to turn colder as CAA eventually
advects into the region. This will drop highs into the upper teens
to lower 20s with overnight lows in the single digits.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Tuesday Night)
Issued At 1005 PM MST Mon Dec 8 2025

VFR conditions are expected through 09/12z. A strong cold front
will move through Tuesday bringing strong, gusty northwest winds
behind it, reaching 50-55kts on the western SD plains at times
after 09/15z. Areas of MVFR/IFR conditions due to lower
clouds/ra/sn will affect northeastern WY/northwest SD behind the
front. Mainly VFR conditions expected over southwest into south-
central SD.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...High Wind Warning from 8 AM MST /9 AM CST/ Tuesday to 2 AM MST
     /3 AM CST/ Wednesday for SDZ001-002-012>014-025>027-030>032-
     041>044-046-047-049-072>078.
WY...High Wind Warning from 8 AM Tuesday to 2 AM MST Wednesday for
     WYZ060.
&&

$$

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