407
FXUS63 KUNR 031115
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
515 AM MDT Wed Sep 3 2025

.KEY MESSAGES...

- Lingering precipitation ends today, but smoke remains
- Strong dry cold front Thursday brings gusty northwest winds (40-55mph)
  with elevated fire danger

&&

.DISCUSSION...(Today Through Tuesday)
Issued at 157 AM MDT Wed Sep 3 2025

07z surface analysis had cold front from central NE through the
Black Hills into south-central MT, slowly moving southwest. Behind
it, smoke has invaded along with isolated/scattered shra/TS in
response to fast moving shortwave over the eastern Dakotas per
water vapour loop. Mostly clear skies west of the precipitation,
but low clouds starting to fill in behind showers per nighttime
microphysics RGB over southwest ND/northwest SD.

Today/tonight, shortwave zips away with support for lingering
precipitation on the wane. REFS guidance indicates persistent
smoke. Temperatures will be near guidance, but could end up being
a little lower if smoke thickness/opacity higher than
anticipated.

Thursday, another shortwave rips across central Canada into the
northern Plains. It will drive a strong dry cold front through the
CWA during the day, but not before temperatures pop into the 80s
ahead it across the southern half of the area. Moisture will be
scant. 800mb winds forecast in the 30-45kt range with
deterministic model consensus showing the best isallobaric forcing
(4-7mb/3hr pressure rises) north/east of the CWA. This is
reflected in probabilities of >55mph wind gusts <20% the western
SD plains per HREF/LREF with EFI SoT north/east of the CWA. NBM
outlier with noticeably higher probabilities (30-50% chance
>55mph), but this is likely a reflection of stronger GEFS wind
forecast. Forecast Bufkit sounding momentum transfer calculations
show same story. For now, it looks like a solid Wind Advisory
event, so will let day shift take one last look at it before
hoisting headlines. Temperatures will be near guidance, but might
be too warm post frontal depending on eventual timing.

Cooler temperatures Friday will be replaced by a slow warming
trend per upper/thermal ridge working into the northern Plains
into early next week. Minimal chances for significant
precipitation per ensemble guidance.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Thursday Morning)
Issued At 513 AM MDT Wed Sep 3 2025

Areas of IFR/MVFR stratus will affect parts of northeastern
WY/northwest SD (including the KGCC/KRAP terminals) this morning.
Conditions will improve this afternoon, but FU will be around with
local MVFR VSBYS. shra/TS over south-central SD will end today.
VFR conditions should prevail tonight.

&&

.FIRE WEATHER...
Issued At 157 AM MDT Wed Sep 3 2025

A dry cold front will move through Thursday. Minimum relative
humidities will dip into the 20s with gusty northwest winds from
40-55mph. Elevated fire danger is expected, especially for the
fine fuels of the grasslands. The Grassland Fire Danger is
forecast high to extreme for Thursday afternoon on the western SD
plains.

&&

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

$$

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