853
FXUS63 KUNR 042327
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
427 PM MST Wed Dec 4 2024

.KEY MESSAGES...

- Cold front sagging southward this afternoon with breezy winds
  and cooler temperatures behind it.

- Front sloshes back eastward with mild temperatures returning
  for the latter half of the week.

- A quick moving shortwave plus an influx of Pacific moisture
  will bring chance for light rain/snow Sunday into early Monday.
  Best chance of accumulating snow across the Black Hills
  (probability of >1" snow ~65% for the Black Hills).

&&

.DISCUSSION...(This Evening Through Wednesday)
Issued at 148 PM MST Wed Dec 4 2024

Upper level analysis shows brisk northwesterly flow aloft with a
departing shortwave trough pushing into IA. Further upstream,
another shortwave trough is pushing through southwestern SK into MT.
A surface cold front stretches from central MT through NE WY,
southeastward along the SD/NE border. Behind the front,
temperatures are in the teens to mid 20s (ND into central SD)
with 40s to near 50 across far western SD into NE WY. Gusty NW
winds behind the front (gusts 25-35 mph) across much of western
SD. The strongest winds are expected across south-central SD (with
gust potential to 50 mph), although winds have yet to fully
materialize. The strongest pressure rises (3-4+ mb/3 hr) are
displaced east of the forecast area, where the strongest winds
have been observed. However, will keep the Wind Advisory in place
for south-central SD where transient 40-50 mph gusts are possible
through the afternoon.

Tonight - the frontal boundary will stall across the SW portion of
the forecast area with cold overnight temperatures from NW SD into
south-central (teens to ~10F). The shortwave trough currently in SK
will clip the far NW after midnight tonight. While mid-level
moisture will be plentiful, low-level moisture will be lacking. Main
sensible impact will be increased cloud cover across NW SD, although
a few spotty flurries will be possible overnight.

Westerly flow will return Thursday, slowly pushing the baroclinic
zone back eastward. Cool and cloudy for NW SD into south-central SD
Thursday with mostly sunny skies and warmer air (upper 30s to
40s) for far western SD into NE WY. Mild and dry weather Friday
into Saturday with the warmest temperatures expected Saturday ->
upper 40s in the Black Hills with widespread 50s across NE WY and
western SD. Warm downslope flow may result in temperatures in the
low 60s across the eastern foothills (Spearfish to Sturgis,
southward to Rapid City and Hermosa/Fairburn).

A quick moving, potent shortwave trough will drop through the
Pacific NW Saturday, pushing into the Northern Plains Sunday. An
influx of Pacific moisture will arrive just ahead of this system
with forecast precipitable water values around 150-200% of normal
Sunday. This influx of moisture coupled with broad large-scale
ascent and some upslope enhancement will yield rain/snow
potential for portions of the area. The best chance for
accumulating snow will be across the Black Hills, where the
probability of >1" snow is ~60-65%. There remains large spread
among the various ensemble members with respect to total QPF for
the event; lingering uncertainty regarding the best overlap of
large-scale forcing with sufficient moisture before drier air
filters into the region Monday.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Thursday Evening)
Issued At 424 PM MST Wed Dec 4 2024

A band of mainly VFR CIGS (4-7kft agl) with local MVFR/IFR CIGS
over/near the northern Black Hills will persist from southeastern
MT through central NE overnight. KRAP/KGCC terminals should remain
VFR through the period. The lower VFR CIGS will lift Thursday as
some mid-level clouds pass by.

&&

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

$$

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