791
FXUS63 KUNR 300154
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
754 PM MDT Wed Jul 29 2026

.KEY MESSAGES...

- Marginal to Slight (Level 1-2 out of 5) risk of severe
  thunderstorms this evening with the primary risk of damaging
  winds, but large hail may also occur.

- Hot weather (Sunday looks hottest) will continue through Monday
  with a Heat Advisory through early this evening.

- Active thunderstorms possible Thursday/Friday, then perhaps a
  lull for the weekend, and then back to active for early next
  week.

&&

.DISCUSSION...(This Afternoon Through Tuesday)
Issued at 1106 AM MDT Wed Jul 29 2026

16z surface analysis had trough from eastern MT to central CO.
Water vapour loop had upper ridge from NM into eastern MT/WY with
a couple of ridge-riders over southeast MT and western WY/UT.
0.5km 1-minute visible satellite loop showed most activity was
elevated at this point, although there is a CU field over south-
central SD associated with oppressive Td/s in the lower 70s.
Effects of these features the main short term forecast concern.

This afternoon/tonight, heat indices will be in the lower 100s
east of the Black Hills so hoisted a Heat Advisory earlier to
account. Main shortwave rotates around upper ridge later this
afternoon and evening. At least 1-2KJ/kg MLCAPE pools ahead of
surface trough with 25-35kts of effective shear forecast. Bufkit
soundings suggest damaging winds would be the main threat with
severe convection (marginal to slight (1-2 out of 5)) risk over
CWA, highest over northwestern SD. Latest CAMs/HREF emphasize this
thinking. So, expect a couple clusters of severe convection this
afternoon/evening moving across the CWA. If cold pools can
congeal, could see a line of severe thunderstorms for a period
which some CAM solutions suggest. Activity will weaken overnight,
but decent low level jet likely to sustain convection.
Temperatures will be near guidance.

Thursday, compact mid-level circulation moves across the CWA with
continued chances for thunderstorms as a cold front slices
through the area leading to "cooler" temperatures. Cold front may
be focus for active/severe thunderstorms Thursday afternoon over
south-central SD. Temperatures will be near guidance.

Lingering PoPs Friday given way to robust thermal ridge expansion
for the weekend with Sunday highs from 100-110F putting pressure
on some records. Mostly dry, but it is the northern Plains, so
thunderstorms cannot be completely ruled out. Next week looks
"cooler" as upper ridge flattens and west/northwest flow aloft
develops, sure to provide shortwaves to create daily chances of
thunderstorms. Confidence is growing for the brief cooldown.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Thursday Evening)
Issued At 754 PM MDT Wed Jul 29 2026

A line of strong to severe thunderstorms with brief cig/vsby drops
to MVFR and borderline IFR will continue east across western South
Dakota over the next several hours, now starting to pull east of
KRAP. Wind gusts to 50kts will remain possible with the stronger
segments and cores along this line. High-res CAMs offer varying
solutions on possible additional scattered showers and
thunderstorms overnight tonight across the region behind this main
line, with a low forecast confidence. For now we continue PROB30
groups to cover some of this activity at KGCC and KRAP. Brief
drops to MVFR will remain possible under any cores overnight.
Breezy NNW winds are expected Thursday with gusts to 20-25kts. At
least isolated thunderstorms appear likely during the afternoon,
but confidence in timing and placement is currently low. PROB30s
may eventually be needed.

&&

.FIRE WEATHER...
Issued At 1106 AM MDT Wed Jul 29 2026

Elevated fire weather conditions are expected this week due to
hot temperatures as well as minimum relative humidity in the teens
and 20s. Hotter weather develops for the weekend with even drier
air (MinRH as low as 8%), so critical fire weather conditions are
likely. Thunderstorm chances highest this afternoon through Friday
and then early next week. The cores of thunderstorms that occur
through Friday should contain wetting rain, but lightning strikes
outside of the cores as well as strong, erratic winds may create
opportunities for new fires.

&&

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

&&

$$

DISCUSSION...Helgeson
AVIATION...KSmith
FIRE WEATHER...Helgeson