280
FXUS63 KUNR 020834
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
134 AM MST Tue Dec 2 2025

.KEY MESSAGES...

- Upslope-enhanced snowfall for the northern/Wyoming Black Hills
  through early Wednesday
- Thursday through early next week, northwest flow aloft will
  push a series of disturbances through the region bringing
  periodic chances for light precipitation

&&

.DISCUSSION...(Today Through Monday)
Issued at 131 AM MST Tue Dec 2 2025

08z surface analysis had low over central SK with a warm front
into western NE, just about through the far eastern reaches of the
CWA. Water vapour loop had upper trough over western Canada into
the Pacific northwest with 140kt jet streak zipping over the
western BC coast. Lead shortwave energy over MT/ID creating some
light radar returns, some of which area starting to brighten as
they hit the higher elevations of the northern/Wyoming Black
Hills. Upper trough and upslope the the main forecast concerns in
the short term.

Today/tonight, upper trough moves southeast with the main pieces
of energy passing well to our southwest and to our northeast.
Synoptic forcing rather light with weak QG-forcing/low level
frontogenesis. Canadian surface low will drag a cold front
through the area later today/tonight, which will focus the main
QPF chances for the plains. Not expecting much QPF on the plains
with rain mixing in east of the Black Hills ahead of the cold
front, quickly changing to snow behind it. The main story will be
the upslope enhancement for the northern/Wyoming Black Hills.
Froude numbers already above 1 early this morning with increasing
0-2km RH today, becoming saturated tonight. Forecast soundings
suggest the best upward vertical motion will be in the dendritic
growth zone tonight, which will fluff up the snow. Latest HREF
LPMM 24-hour QPF gives about 0.50" liquid equivalent precipitation
by Wednesday morning. HREF probabilistic depictions show 70-100%
chance >0.25" QPF and 50% chance 0.50" QPF. Subjective pattern
recognition and high resolution deterministic model output suggest
these values reasonable. Will hoist a Winter Weather Advisory for
the northern/Wyoming Black Hills to account. Considered putting
headlines up for northern Campbell/Crook County Plains, but not
coming up with enough snow/impacts to issue at this time.
Isallobaric forcing behind the cold front supports breezy/locally
windy spots. Temperatures will be near guidance.

Wednesday will 10-20F colder than today with a bit of snap in the
air per northwest winds averaging 12-22 mph. Upslope snow should
quickly wane in the morning.

The rest of the forecast looks unsettled as northwest flow aloft
propels a series of disturbances through the northern Plains.
We`ll be on the edge of the warmer air initially, but the latest
ensemble guidance shows a slow warming trend into early next week,
albeit with increasing temperature spreads. Best chance of
accumulating snow will continue to be over the northern Black
Hills given expected boundary layer flow regime.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Tuesday Night)
Issued At 1012 PM MST Mon Dec 1 2025

An approaching system will bring increasing high and mid-level
clouds to the area this evening with chance of snow showers in the
Black Hills after 08-10z. More widespread precipitation chances
overspread the area after 16-18z from west to east with MVFR/IFR
and transient LIFR conditions in low clouds and snow.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory from noon today to 6 AM MST Wednesday
     for SDZ024.
WY...Winter Weather Advisory from noon today to 6 AM MST Wednesday
     for WYZ057.
&&

$$

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