349
FXUS63 KUNR 132309
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
409 PM MST Mon Jan 13 2025

.KEY MESSAGES...

- Light snow tonight and Tuesday with the highest accumulations
  over the northern Black Hills
- Warmer mid-week
- Arctic air this weekend into early next week

&&

.DISCUSSION...(This Evening Through Monday)
Issued at 154 PM MST Mon Jan 13 2025

The upper low, and associated surface low, has dropped southward
into northern Minnesota this afternoon and is currently swinging
an upper trough across the Dakotas producing areas of light snow.
A couple more disturbances will cross the forecast area tonight
into Tuesday with each one bringing weak QG/frontogenetic forcing,
particularly along the stationary boundary in place along the
eastern parts of the forecast area.

Deep layer moisture is limited, however could see 1 to locally 2
inches of snow on the plains tonight through Tuesday morning.
Boundary layer flow generally supports Froude numbers >1 and
0-2km RH >90% over the northern Black Hills until around 18z
Tuesday. HREF has 60% chance >0.40" QPF over the highest
elevations of the Black Hills and 70-90% chance 0.25" QPF. Looks
like a good recipe for 4-8" of snow. Bufkit soundings depict a bit
more westerly component to the wind than is usual in upslope snow
events, so the highest total snow accumulations are expected to
be displaced more toward the western edge of the hills, between
Cheyenne Crossing, Buckhorn, and Moskee. A Winter Weather Advisory
remains in effect over the northern Black Hills.

For Wednesday and Thursday, an east-west oriented upper ridge
will flop southward across the northern plains. A surface warm
front will promote warming westerly downslope flow. Milder
temperatures will develop, particularly on the eastern slopes of
the Black Hills and the adjacent plains, where high temperatures
around 50F area possible, per ensemble guidance.

For the coming weekend, confidence is high that a deep upper
trough will drop southward over the eastern 3/4ths of North
America opening the door for arctic air to spill into the northern
Plains. Some light snow will occur. Temperatures will be 20-30F
colder than average but the coldest air will be east of the CWA.
Apparent temperatures may be cold enough for the issuance of
Extreme Cold products, but right now, record-breaking cold is not
anticipated per EFI/NBM guidance.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Tuesday Evening)
Issued At 405 PM MST Mon Jan 13 2025

MVFR/IFR ceilings with some light snow/flurries will persist
across the plains of western South Dakota from far northwestern
South Dakota into south central South Dakota. KRAP terminal may
see brief period of MVFR ceilings through early evening, but
confidence is low. MVFR/IFR conditions with snow will also
continue for the northern Black Hills through Tuesday morning. A
brief period of light snow is possible over northeastern Wyoming
tonight, impacting the KGCC terminal.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory until 11 AM MST Tuesday for SDZ024.
WY...Winter Weather Advisory until 11 AM MST Tuesday for WYZ057.
&&

$$

DISCUSSION/KEY MESSAGES...10
AVIATION...7