Box Elder, South Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

320
FXUS63 KUNR 231734
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1034 AM MST Mon Dec 23 2024

.KEY MESSAGES...

- Slight chances for freezing fog/drizzle across northwestern SD
  tonight

- Warm temperatures and mostly dry conditions expected through
  Christmas

&&

.DISCUSSION...(Today Through Sunday)
Issued at 318 AM MST Mon Dec 23 2024

Short wave ridging has built across the northern Rockies with dry
air filtering into the region behind a weak shortwave. Skies
across the CWA are clear with temperatures ranging from the teens
to low 20s across the plains and portions of the Black Hills to
the upper 30s to low 40s across the eastern and southern slopes of
the Black Hills. Pleasant and mild day on tap as shortwave ridge
axis moves across the region, temperatures will rise into the
upper 40s to low 50s by this afternoon.

Shortwave trough crosses the CWA early Tuesday. Ahead of the
trough, weak Q-vector convergence and period of ample deep layer
moisture will result in spotty light precipitation - mainly across
northeastern WY, the Black Hills, and northwestern SD. BUFKIT
soundings across northwestern SD indicate a shallow layer of very
moist air near the surface which could lend to the development of
fog/freezing fog. Weak shear at the top of the saturated layer
would support freezing drizzle in some areas as temperatures drop
below freezing tonight into early Tuesday. Forecast confidence in
this scenario is low as the saturated layer near the surface is
very shallow -- however have opted to mention slight chances for
freezing drizzle across northwestern SD for this forecast package.
HREF grand ensemble probs do show decent chances of dense fog
(50-80% probabilities of visibility <0.5 miles) along the eastern
boundaries of our CWA (so eastern Ziebach County down to Tripp
County) tonight into early Tuesday morning. Probabilities of dense
fog decrease further west but there are areas of 20-40%
probabilities across northwestern SD into the Black Hills.

If precip does occur tonight, chances for measurable precip
(greater than 0.01") are very low with the HREF grand ensemble
painting 10- 30% probs across northwestern SD into the northern
Black Hills and northeastern WY for tonight through early Tuesday.
The LREF grand ensemble seems even more pessimistic about our
odds with chances across northwestern SD < 5% and 0-10% across
northwestern WY.

Shortwave ridging builds into the region by Christmas with
southerly return flow advecting warm air into the CWA. A weak
shortwave will cross the region Christmas Day, though moisture
with this system will be minimal - keeping precip chances near
zero. A brief period of upslope enhancement combined with modest
0-2km RH (~70-80%) could support the development of a few snow
showers in the northern Black Hills. Chances for any measurable
snow will be very low (LREF grand ensemble paints 0-20% probs
across the Black Hills).

Progressive upper level pattern continues through the rest of the
week into the weekend with deterministic guidance in poor
agreement as to location, timing, and strength of any systems.
This translates to low confidence in pattern evolution and thus
sensible weather impacts through the rest of this year.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Tuesday)
Issued At 1033 AM MST Mon Dec 23 2024

VFR conditions are likely for most of the area thru the period.
However, IFR/LIFR cigs/vsbys in BR/FG are possible along and east
of a KHEI to KICR line beginning around 00z. Modest improvement
is then expected from north to south thru the end of the period.

&&

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

$$

DISCUSSION/KEY MESSAGES...Wong
AVIATION...Dye