595
FXUS63 KUNR 120807
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
207 AM MDT Mon May 12 2025

.KEY MESSAGES...

- Unseasonably warm temperatures through Tuesday with more record
  highs today
- Elevated/near critical fire weather conditions through Tuesday
- Unsettled weather pattern will start Tuesday night, persisting
  through the end of the forecast period with good chances for
  beneficial QPF

&&

.DISCUSSION...(Today Through Sunday)
Issued at 203 AM MDT Mon May 12 2025

07z surface analysis had trough from western ND into eastern WY.
Water vapour loop had weakening upper ridge from the Midwest into
the southwest CONUS and upper trough/low coming onshore via WA/OR.
Leftover weak returns per regional radar loop over the CWA, but
most echoes virga. Disposition of the upper trough/low the main
forecast concern.

Today/tonight, upper trough moves into the northern Rockies. Cold
front develops ahead of it with deep southwest flow over the CWA,
which will maintain/slightly increase low level thermal ridge.
EFI continues to show MaxT today in the 90-100th percentile which
translates to another day of record highs. 100F isn`t out of the
question east of the Black Hills toward central SD. Lower
tropospheric kinematic fields don`t look as favorable for wind
advisory speeds (HREF <20% chance 45mph gusts) as they did
yesterday for south-central SD, so will hold off on headlines. Dry
air/cap should prevent PoPs.

Tuesday, upper trough slowly moves eastward as cold front reaches
the western half of the CWA and then stalls per parallel flow
aloft. Ensemble guidance gives 70s behind the front and 80s/lower
90s ahead of it, but confidence near the front on the lower side
given uncertainty in eventual position. It still looks too
dry/capped for daytime PoPs, but increasing moisture/QG-forcing
ahead of upper trough will move into the CWA Tuesday night with
increasing chances for showers/thunderstorms.

Wednesday/Thursday, upper trough rotates through the northern
Plains with deepening surface low ahead of it and developing gusty
northwest winds, especially Thursday (50-90% chance >45mph gusts)
when headlines may be needed. Ensembles show main forcing/QPF has
shifted a bit northwest with the highest QPF from northeast WY
into far northwest SD. NBM continues to show a south-north
gradient of chance for >0.50" 48-hour QPF of 30-70%. Entire CWA is
painted by 70-100% chance >0.1" QPF. Temperatures will be
significantly modulated by amount of clouds/QPF duration, so
confidence not particularly high for actual values but eventually
will end up below normal by Thursday.

Friday through Sunday, weakly unsettled weather foreseen given
progressive upper flow and embedded wiggles. More significant
upper trough arrives for early next week with the potential for
beneficial QPF and maybe some snow for some folks.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Monday Night)
Issued At 1014 PM MDT Sun May 11 2025

VFR conds through the period. ISOLD SHRA will dissipate through
early morning. Breezy southerly winds will continue through
Monday.

&&

.FIRE WEATHER...
Issued At 203 AM MDT Mon May 12 2025

Minimum relative humidities today will be 10-20% with deeply
mixed boundary layer supporting gusty south/southwest winds,
especially in the afternoon/early evening. Temperatures/low
relative humidities will be tempered Tuesday, but still elevated
east of the Black Hills. Thus, elevated/near critical fire weather
conditions continue today and then Tuesday ahead of the cold
front. Locally critical conditions may occur where fuels are still
receptive, but green up is here per land manager input/GOES-19
NDVI remote sensing.

Upper trough moves through Tuesday night through Thursday with
increasing chances for wetting rains, gusty northwest winds, lower
temperatures, and higher relative humidities. Unsettled weather
continues through the end of the forecast with perhaps a more
impactful system for early next week.

&&

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

$$

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