909
FXUS63 KUNR 191905
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
105 PM MDT Wed Aug 19 2026

.KEY MESSAGES...

- Upper ridge will dominate the weather through early next week
- Thunderstorm chances will be very limited through Saturday
  afternoon
- Temperatures will average about 4-8F above normal

&&

.DISCUSSION...(This Evening Through Wednesday)
Issued at 1259 PM MDT Wed Aug 19 2026

18z surface analysis had a weak trough from eastern MT into
western WY. 0.5km visible loop depicted a weak outflow boundary/CU
over south-central SD in a regime characterized by little MLCIN
per latest SPC mesoanalysis. Water vapour loop had upper ridge
over the Rockies with northwest flow aloft over the northern
Plains. A couple of weak wiggles noted, but nothing substantial.

Late this afternoon/evening, a stray shra/TS may develop over
south-central SD along the boundary so have added 15% PoPs to
account. Tonight into Thursday, aforementioned trough slips
through the CWA with northwest winds behind it. Moisture is
limited over the CWA, so don`t expect any precipitation until the
boundary exits the area and taps into better moisture over
NE/southeast SD. These thoughts are in line with latest CAM
guidance. Temperatures will be near guidance.

Friday through Saturday afternoon, upper ridge builds more
strongly into the northern Plains with height rises generally
suppressing convective chances, but wouldn`t be surprised if
something bubbles over the Black Hills during peak insolation.
Saturday night through early next week, a series ridge-riders will
bring periodic chances for tsra, but coverage will be hit-or-miss
and many folks might not get anything. Temperatures a bit tricky
per low confidence in cloud-cover/PoPs, but 4-8F above normal in-
line with probabilistic guidance.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Thursday)
Issued At 1111 AM MDT Wed Aug 19 2026

VFR conditions are expected through the TAF period.

&&

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

$$

DISCUSSION...Helgeson
AVIATION...Schultz