283
FXUS63 KUNR 270808
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
208 AM MDT Thu Mar 27 2025

.KEY MESSAGES...

- Critical fire weather conditions over northeastern Wyoming this
  afternoon
- Mild today and Friday
- Increasing confidence in beneficial precipitation Friday night
  through Sunday, but low confidence in snow amounts

&&

.DISCUSSION...(Today Through Wednesday)
Issued at 159 AM MDT Thu Mar 27 2025

07z surface analysis had low over northeastern WA with frontal
boundary into far northern NE, which is a weak back door cool
front over western SD. Water vapour loop had upper ridge building
into the northern Plains creating clear skies over the CWA. Large
upper low spinning off the northwest CONUS coast will be the main
weather maker through the weekend.

Today through Friday afternoon, upper low moves into the Pacific
northwest, flattening the upper ridge as it moves eastward and
southwest flow develops. Northern ID low moves southeast pushing
backdoor front eastward as a warm front today with trailing cool
front later Friday. Mild couple of days on tap, although gusty
southeasterly winds will develop over northwestern SD today,
becoming northwesterly Friday. Temperatures will be warmest over
the southwest half the area today and southeast half Friday as
temperatures soar into the 70s.

Friday night through Sunday, expect southwest flow aloft as upper
trough spins a couple of shortwave troughs into the northern
Plains. First trough arrives late Friday through Saturday
afternoon. Aforementioned cool front stalls over far southwest
reaches of the CWA and will be the focus of increasing PoPs Friday
night (per theta-e advection, frontogenesis band) as first
shortwave trough moves into the CWA. Lift rapidly decreases
Saturday afternoon. Forecast soundings support rain initially, but
as diurnal cooling, low level cold air advection, and dynamic
cooling conspire, some snow expected by Saturday morning,
especially over the higher elevations of the Black Hills into
northwestern SD. Second shortwave trough arrives later Saturday
night, persisting into Sunday. Colder air will already be in
place, so expect more snow out of this wave. Combined, these
systems should bring beneficial QPF to the CWA with near 100%
chance >0.1", 70-90% chance >0.25", and 50% chance >0.50".
Marginal temperatures for first wave gives low confidence for
snow accumulation, but a few inches likely from the northern Black
Hills into northwestern SD. Given antecedent temperatures, unless
snow comes down in buckets, might be hard to get much to
accumulate on lower elevation road surfaces during both days.

Next week looks unsettled as progressive flow brings a series of
shortwave troughs across the northern Plains. Low level baroclinic
zone near/in the CWA which will give focus to precipitation
chances and low confidence for temperatures. Ensemble guidance
depicts 20-30F temperature spreads Tuesday through Friday for
MaxT.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Thursday Night)
Issued At 930 PM MDT Wed Mar 26 2025

VFR conditions are expected through the period.

&&

.FIRE WEATHER...
Issued At 159 AM MDT Thu Mar 27 2025

Expect critical fire weather conditions this afternoon over
northeastern WY. Highs in the 70s, MinRH around 15 percent, and
southwesterly wind gusts around 30 mph are expected. Additionally,
very dry/well-mixed boundary layer (unstable low levels) with
some mid-level moisture may result in spotty virga showers during
the afternoon. Confidence is low in the development of virga.
Should virga develop, gusty, erratic winds will occur. Elevated
fire weather conditions are expected elsewhere, lasting into
Friday. A couple of upper level disturbances will bring excellent
chances for wetting precipitation for the weekend, including a few
inches of snow from the Black Hills into northwestern SD.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...Red Flag Warning from noon today to 6 PM MDT this evening for
     WYZ314>317.
&&

$$

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