143
FXUS63 KUNR 182317
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
517 PM MDT Sat Jul 18 2026

.KEY MESSAGES...

- Hot through the weekend with elevated to near critical fire
  weather conditions.

- Isolated strong storms this afternoon/evening. A marginal risk
  (1 out of 5) of severe storms Sunday afternoon/evening.

- Slightly cooler conditions finally look to return next week.

&&

.DISCUSSION...(This Evening Through Saturday)
Issued at 1254 PM MDT Sat Jul 18 2026

Upper ridging continues the western CONUS, with several upper waves
approaching the region from the west/southwest. Surface obs show
temps have been lagging in the 70s and 80s, but are now rising
quickly since the low clouds dissipated. Dewpoints are still well
into the 60s across western SD within deep southeasterly flow. Have
dropped max temps today to the low to mid 90s across most locations.
Still looking at some afternoon and evening storms today. SBCAPE of
~1200 J/kg is expected within the corridor from SCentral SD through
the Black Hills into parts of NE WY/NW SD. The next wave is
approaching from NCentral and will cross NE WY/NW SD this evening.
Shear is strongest across NW SD, where southeasterly low level winds
are strongest. Storms are expected to initiate across the Black
Hills this afternoon...then NE WY/SE MT in the late afternoon/early
evening. As storms track into NW SD just north of the Black Hills,
could see a storm or two with gusty winds/hail. These storms will
continue eastward toward a less favorable environment over NCentral
SD, where both instability and shear weaken. The thermal ridge over
the central/northern Rockies will slide eastward overnight tonight
toward the CWA, bringing back very hot temperatures. Highs on Sunday
will be in the triple digits. Dewpoints will be more reasonable
(50s) but will still result in advisory threshold heat index. Will
not make any changes to heat-related headlines. A cold front will
cross MT and push into ND late Sunday, which will result in
strong/severe storms over those areas. By the time the front gets to
NW SD, it seems to stall before resurging southward early Monday
morning. Still unclear with the severe weather threat Sunday
afternoon. It appears the bulk of severe storms will be north and
east of the CWA. Good instability and somewhat decent shear will be
present, but the forcing with the frontal boundary might be missing.
Regardless, could still see convection develop from transient
outflow boundaries or orographically from the Black Hills and
Bighorns. Any storms that develop may be severe, but think better
organization will be limited to areas east of the CWA where
increased forcing/shear will be present. Cooler Canadian high
pressure will build across the northern Plains for the first half of
the week. Uncertain about max temps Monday behind the cold front,
which does seem to struggle pushing out the very warm H85 temps.
Could still be a hot day on Monday, but wouldn`t be surprised if it
ends up being a tad cooler than what the NBM shows. Better cold air
advection is expected Monday night into Tuesday should bring lower
temps...but we`ll likely still see highs in the upper 80s to lower
90s. Better chances for precip are expected for the second half of
next week.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Sunday Evening)
Issued At 515 PM MDT Sat Jul 18 2026

Isolated thunderstorms have developed over the Black
Hills/northeast WY late this afternoon. The overall motion of
these storms will be to the east. That being said, these storms
should fade out quickly once they track far enough away from the
mountains. Gusty, erratic winds and brief heavy rain will occur
with any storm along with local IFR conditions.

Outside of those storms, mainly VFR conditions are expected
through the TAF period.


&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory until 9 PM MDT /10 PM CDT/ Sunday for SDZ001-002-
     012>014-025>027-030>032-041>044-046-047-049-072>078.
WY...Heat Advisory until 9 PM MDT Sunday for WYZ054>056-058>060.
&&

$$

DISCUSSION...13
AVIATION...GS