063
FXUS63 KUNR 310926
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
226 AM MST Fri Jan 31 2025

.KEY MESSAGES...

- Dry/mild conditions through Saturday. Locally gusty winds and
  low relative humidity will result in elevated fire weather
  conditions on Saturday

- Strong cold front arrives early Sunday with gusty winds and
  falling temperatures. Much colder air remains across the area
  for most of next week

- Widespread accumulating snow likely Sunday night into Monday
  with 40-70% probability of accumulations ranging from 2" to 5".
  Low to moderate confidence in the location of greatest snowfall
  accumulation.

&&

.DISCUSSION...(Today Through Thursday)
Issued at 215 AM MST Fri Jan 31 2025

Current surface map places weak back door cold front across
southwestern North Dakota into central South Dakota. Cold front
backs into northwestern South Dakota early this morning then
stalls. Area of low stratus in central North Dakota is expanding
southwestward. RAP/HRRR soundings suggest this low stratus may
make it into far northwestern South Dakota around 12Z and linger
through much of the morning. Position of front and stratus/fog
will result in wide range of temperatures this afternoon with
highs in the lower 30s near the North Dakota border and lower 50s
in southwestern South Dakota.

Fast zonal flow sets up across the area this weekend as upper trof
digs across the Pacific Northwest. Fast moving shortwave crosses
the area late Saturday/Saturday night. Surface low consolidates
over North Dakota Saturday. West/southwest winds and low relative
humidity will result in elevated fire weather conditions,
especially across the southern Black Hills and southwestern South
Dakota plains. Strong cold front dives across western South
Dakota Saturday night. 3-5mb/3h pressure rises behind the cold
most offront will support a period of gusty northwest winds
Saturday night through early Sunday.

Attention turns to snowfall potential Sunday night through
Monday. Low level baroclinic zone stalls out over the forecast
area with 120-150kt jet overhead. Next impulse crosses the area
Sunday night/Monday with a period of isentropic lift/frontogenesis.
Widespread light snow is likely across the area. With banded
nature of the strongest lift, pinning down location of highest
snowfall amounts is uncertain at this time. 00Z LREF probability
of QPF >0.25" is 40% to 70% across northeastern Wyoming and
western South Dakota...highest from the Black Hills into
northwestern South Dakota. This is a northward shift from the 12Z
LREF which had the higher probabilities from the Black Hills into
southwestern South Dakota. Thermal profiles suggest snow ratios
of 15:1 to 20:1, which supports snowfall accumulations of 3" to 5"
wherever the best forcing sets up.

Cold temperatures continue through the rest of the week with
additional light snow accumulations possible.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Friday Night)
Issued At 127 AM MST Fri Jan 31 2025

There is a chance (40-50%) for an area of low stratus/fog to
impact far northwestern South Dakota from 12Z-18Z today. IFR/LIFR
conditions would occur in the low stratus/fog. VFR conditions are
expected elsewhere through the forecast period.

&&

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

$$

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