287
FXUS63 KUNR 181843
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1243 PM MDT Tue Aug 18 2026

.KEY MESSAGES...

- Storms will develop over the area this afternoon, some storms
  may be strong to severe and be capable of 70+ mph gusts and
  large hail.

- More chances for afternoon storms on Wednesday, mainly across
  western SD.

- Trending warmer to end the week into next weekend.

&&

.DISCUSSION...(This Evening Through Tuesday)
Issued at 1242 PM MDT Tue Aug 18 2026

Shortwave will push through region today and bring another round of
storms to the CWA this afternoon. Modestly unstable airmass of 1500-
2000 J/kg MUCAPE will develop over western SD by this afternoon and
evening. The instability combined with 40-50kt bulk shear will
support organized convection and potential severe weather. Main
hazards will be strong wind gusts (some gusts could exceed 70 mph)
and large hail. There is still uncertainty as to the timing and
coverage of convection this afternoon, though right now it looks
like the most likely area for severe storms stretches from
northeastern WY into portions of western and south central SD.

Wednesday is looking drier as rising heights courtesy of the
building ridge to our west will limit convection. We could still see
some isolated storms towards the eastern third of our CWA where 1000-
1500 J/kg MUCAPE will develop by the afternoon.

The upper level pattern shifts after Wednesday as aforementioned
ridge continues to build over the western US and overspreads the
region. Our CWA will sit on the northeastern periphery of the ridge,
meaning we`ll see warmer temps and continued chances for storms
through the end of the week.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Wednesday)
Issued At 1116 AM MDT Tue Aug 18 2026

Isolated/scattered thunderstorms with gusty, erratic winds will
develop after 18/21z, waning by 19/06z. Local IFR conditions will
occur with the strongest storms. Outside of storms, VFR
conditions will prevail through the period.

&&

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

$$

DISCUSSION...Wong
AVIATION...Helgeson