162
FXUS63 KUNR 170838
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
238 AM MDT Thu Apr 17 2025

.KEY MESSAGES...

- Accumulating snow for northeastern WY/Black Hills likely today
  into Friday morning

- Active pattern will bring seasonable temperatures and unsettled
  weather through early next week.

&&

.DISCUSSION...(Today Through Wednesday)
Issued at 237 AM MDT Thu Apr 17 2025

Most recent sfc analysis depicts sfc cold front has pushed
through the CWA with breezy northerly winds developing behind it.
Low level FGEN has triggered light shower development across
northwestern SD into the Black Hills down into southwestern SD.
Precip is very likely rain as sfc temps are still in the mid-40s
to 50s across much of the area. Further up in the atmosphere,
upper level positively tilted trof is located over the northern
Rockies with the trof axis extending from ID/MT into NV/CA. Mid
level water vapor imagery shows plume of Pacific moisture
advecting into the region.

Upper level trof will slide into the region today with the upper
level front and moisture advection supporting the development of
precip across northeastern WY into portions of western SD through
this afternoon. In terms of QPF - HREF proves to be the most
aggressive, painting a 1+" QPF bullseye over the Northern Black
Hills (HREF probs of 1+" QPF range from 60-85%). GEPS/GEFS/Euro
output is a little more conservative with QPF across the Northern
Black Hills at around 0.5". Not sure the moisture coming in will
be sufficient enough to support 1+" QPF, even with upslope
enhancement, so have tamped down on QPF amounts for the Northern
Black Hills with little change to QPF outside of the hills. Low
level CAA will transition the Black Hills and northeastern WY to
snow early today, while other areas can expect rain or a rain/snow
mix. In terms of snow accumulations ... it`s spring, temperatures
have been warm lately, and the bulk of QPF will be falling during
the day. All of those factors are not favorable for impactful
snow accumulation across most of the CWA with the exception of the
Northern Black Hills and Bear Lodge Mtns where WSSI probs for
minor impacts have increased (now at 70-90%). Accumulations of 3
to 6 inches are possible in these areas. Therefore, will continue
the current Winter Weather Advisories. WSSI probs for minor
impacts have increased across northeastern WY as well (80-95%) but
still have very low confidence in snow being able to accumulate
across northeastern WY due to aforementioned reasons. Therefore
will hold off on any advisories for the northeastern WY plains.

In terms of winds - modest 3 hr pressure rises of 2 to 3 mb
through this morning and afternoon will support windy conditions
across the western SD plains. Some spots near Hermosa/Fairburn and
across south central SD could reach low end advsy gusts, though
HREF is showing basically 0% probs for 45+ mph gusts for the CWA
today.

Precip will taper off through Friday with cooler conditions
lingering through the weekend. Southern stream system will graze
the CWA Sunday, bringing low chances of light rain back to our
neck of the woods. Progressive flow expected to continue through
the first half of next week, maintaining seasonable temperatures
and unsettled weather.


&&

.AVIATION...(For the 00Z TAFS Through 00Z Thursday Evening)
Issued At 534 PM MDT Wed Apr 16 2025

VFR conditions are expected through this evening. A cold front
will move through after midnight, bringing some MVFR/IFR/LIFR
conditions and rain/snow to northeastern WY and northwestern SD
after 08Z. Additionally, northwest winds will be 15 to 25 mph
with gusts up to 40 mph with the front. There is a chance for some
VCFG at the KGCC site by 18z.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory from 6 AM this morning to 9 AM MDT
     Friday for SDZ024.
WY...Winter Weather Advisory from 6 AM this morning to 9 AM MDT
     Friday for WYZ057.
&&

$$

DISCUSSION/KEY MESSAGES...Wong
AVIATION...Woodward