193
FXUS63 KUNR 050854
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
154 AM MST Wed Feb 5 2025

.KEY MESSAGES...

- Sharp temperature gradient today will promote gusty winds from
  Wright to Edgemont this afternoon and then in the squeeze zone just
  east of the Black Hills
- Bands of snow will develop Thursday night and affect the area
  Friday with good chances (40-70%) for 4" of accumulation for
  parts of the area

&&

.DISCUSSION...(Today Through Tuesday)
Issued at 149 AM MST Wed Feb 5 2025

08z surface analysis had low over southwest MT with sharp
boundary into southeastern WY. Water vapour loop had fast
southwest flow aloft with weak shortwave over southeast WY
creating some light radar returns over the NE panhandle/far
southern SD. Another wave noted over ID, which will be the main
weather driver today/tonight. Bigger weather maker on tap for
Friday.

Today/tonight, lead weak shortwave sails east/northeast with some
patchy light snow/flurries ending over the southern CWA. Modestly
stronger ID shortwave zips across MT/ND, but it will be moisture-
starved with only low pops warranted in the north. The wave will
enhance southwest MT surface low as it travels southeast along
boundary, bending northward as a warm front into the CWA. How far
north the front makes it will have a massive impact on MaxT this
afternoon. Confidence is low for temperatures on the plains, but
higher for the higher terrain of the Black Hills as well as from
Wright to Pine Ridge where forecast soundings show the shallowest
cold air. Given pressure gradient and forecast soundings, gusty
west/southwest winds (HREF 50-80% chance 50-55 MPH) expected
behind warm front from Wright to Edgemont, so will hoist a Wind
Advisory for western Fall River County. As low passes to the
southeast and trailing cold front sloshes colder air back south,
3-6mb/3hr pressure rises develop, but isallobaric forcing isn`t
completely aligned with the boundary layer wind. Suspect we might
need a Wind Advisory (HREF 30-60% chance gusts >45mph) for the
eastern Black Hills squeeze areas behind the low/cold front this
evening. If the processes sync up better, higher gusts could
occur. Day shift will reassess. Lows will be near guidance
tonight.

Thursday will be seasonally cool, but with some lovely sunshine.

Thursday night through Friday night, upper low off the northwest
CONUS comes ashore and traverses through the northern Rockies into
the northern Plains. Southwest flow ahead of it will promote
increasing isentropic lift along tight low level baroclinic zone.
QG/frontogenetic forcing line up nicely supporting west/east
banded snow field. Latest ensemble guidance has pushed the best
snowfall further north, painting the Black Hills into northwest SD
with a 40-70% chance 4"+ snow as well as 20-50% chance 6"+ snow.
Given the latitude uncertainty and collaboration with neighboring
offices, will forgo Winter Storm Watch tonight, but day shift
will have take a hard look, especially if LREF guidance remains
consistent. Temperatures will be near guidance.

Saturday through the start of next week, colder air seeps in with
readings 10-25F below normal. If Friday`s snowcover is
widespread, colder end of guidance warranted.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 1022 PM MST Tue Feb 4 2025

Areas of MVFR/local IFR conditions will persist through Wednesday
morning, especially around the Black Hills. A strong low level
inversion may result in Low Level Wind Shear overnight into
Wednesday morning. VFR conditions are expected across southwestern
South Dakota for much of Wednesday, with MVFR conditions across
northwestern South Dakota and part of far northeastern Wyoming
into Wednesday evening.

&&

.FIRE WEATHER...
Issued At 149 AM MST Wed Feb 5 2025

Elevated fire danger is expected over snow free areas of southern
South Dakota per gusty west/southwest winds and dead fine fuels.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory from noon today to 7 PM MST this evening for
     SDZ041.
WY...None.
&&

$$

DISCUSSION/KEY MESSAGES...Helgeson
AVIATION...7
FIRE WEATHER...Helgeson