196
FXUS63 KUNR 121751
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1151 AM MDT Tue Aug 12 2025

.KEY MESSAGES...

- Hot by Wednesday/Thursday with elevated to near-critical fire
  weather conditions developing southwest
- Marginal risk (level 1 of 5) of severe thunderstorms Wednesday
  afternoon/evening for western SD

&&

.DISCUSSION...(Today Through Monday)
Issued at 143 AM MDT Tue Aug 12 2025

07z surface analysis had weak high pressure over the CWA behind a
cool front that has exited the CWA via southeast SD/NE. Water
vapour loop depicted northwest flow aloft with a weak wave over MT
which was creating weak radar returns per regional radar loop.

Through Thursday, southwest CONUS upper ridge moves east shifting
northwest flow aloft over the CWA to southwest flow. As this
happens, thermal ridge will expand into the area. First puff
occurs tonight as weak shortwave zips across northern WY with weak
theta-e advection ahead of it, potentially sufficient for
elevated convection late tonight. This wave will support a surface
low over eastern WY Wednesday, bringing southerly return flow
ahead of it and the development of 1-1.5KJ/kg SBCAPE (SPC HREF)
and ~35kt shear. This will be sufficient for isolated
strong/severe thunderstorms mainly east of the Black Hills into
Wednesday evening, but SBCIN should keep coverage low and tied to
terrain/mesoscale features. Additional convection may develop
Thursday night with cap during the day suppressing most activity.
Main severe TSRA focus Thursday will be over the eastern Dakotas
where richer low level moisture is present. Temperatures through
Thursday will be near guidance and hottest Thursday.

Friday into the weekend, expect seasonal temperatures/pops driven
by the ubiquitous shortwave generating machine that is August
southwest flow aloft. Early next week, there are hints that upper
ridge amplifies over the northern Plains which would imply a
return to hotness, but ensemble guidance not particularly
supportive of anything other than "regular" warmth.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 1151 AM MDT Tue Aug 12 2025

VFR conditions are expected through the TAF period. Isolated -TSRA
may develop near the WY/MT and SD/MT/ND border after 13/06z,
affecting GCC first and then RAP toward early morning...but only
reflection in TAFs will be scattered AC around 10kft.

&&

.FIRE WEATHER...
Issued At 143 AM MDT Tue Aug 12 2025

The arrival of a seasonably hot and dry air mass may bring
elevated to near-critical fire weather conditions to portions of
northeastern WY and southwestern SD Wednesday/Thursday. Afternoon
relative humidity values will drop below 20 percent as highs climb
into the 90s in areas with rapidly drying fuels. Winds are
currently forecast to remain marginal for significant fire weather
conditions, but if gusts of 25-30 mph can emerge, near-critical
fire weather conditions would develop. Not enough confidence (need
30-50%) to hoist Fire Weather Watches early this morning.

&&

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

$$

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