993
FXUS63 KUNR 010920
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
220 AM MST Mon Dec 1 2025

.KEY MESSAGES...

- Northwest flow aloft will push disturbances through the region
  through next weekend
- Best chance of accumulating snow will be over the northern
  Black Hills courtesy of northwesterly upslope flow

&&

.DISCUSSION...(Today Through Sunday)
Issued at 216 AM MST Mon Dec 1 2025

09z surface analysis had chilly high over the Midwest with return
flow for the CWA ahead of a developing warm front laid out from
eastern MT into CO. Water vapour loop showed upper trough moving
southeast of the CWA with northwest flow behind it. Regional radar
loop/webcams suggest a few flurries over south-central SD, which
should end by sunrise.

Today/tonight, warm front moves through as winds develop a
westerly component behind it. Temperatures will be near guidance
given downslope flow, even for folks with deeper snow cover.

Tuesday/Wednesday, upper trough races from Canada through the
plains. Energy will split with one shortwave passing to our
northeast with weak QG-forcing and another passing well to our
southwest. Cold front with modest moisture/frontogenesis moves
through, which will be the main forcing mechanism for QPF on the
plains. Precipitation east of the Black Hills will mix with rain
Tuesday afternoon, but mostly snow elsewhere and then all snow
behind the cold front. For the northern Black Hills, Froude
numbers >1 by Tuesday evening with 0-2km RH reaching 90%. A good
setup for upslope-enhanced snowfall. Latest LREF guidance
suggests several at least a couple inches of snow (>70% chance
>0.10" QPF). <30% chance of >0.10" QPF on the plains. Not thinking
Winter Weather Advisory headlines at this point with total QPF
chances >0.25" <30%. High resolution deterministic guidance more
bullish, however, so will take a close look at the latest guidance
today. Relatively mild temperatures Tuesday are squashed behind
the cold front Tuesday night leading to highs 10-20F below normal
for Wednesday.

Additional disturbances move through Thursday night to the
weekend with the northern Black Hills favored for the best QPF.
The plains best chance will be Friday night/Saturday when synoptic
forcing perks up. Didn`t stray from guidance for temperatures,
but spreads do expand quite a bit at the end of the period giving
low confidence for "mild" vs "cold".

&&

.AVIATION...(For the 06Z TAFS Through 06Z Monday Night)
Issued At 1030 PM MST Sun Nov 30 2025

Areas of low stratus and flurries remain possible overnight along
the SD/NE border into SW SD with transient MVFR/IFR conditions
possible. Otherwise, VFR conditions expected through the forecast
period.

&&

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

$$

DISCUSSION/KEY MESSAGES...Helgeson
AVIATION...SE