858
FXUS63 KUNR 120544
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1144 PM MDT Tue Aug 11 2026

.KEY MESSAGES...

- Becoming unsettled and cooler.

- Wildfire smoke is expected to linger much of the week, with
  thicker smoke at times across the western third

&&

.UPDATE...
Issued at 1143 PM MDT Tue Aug 11 2026

Intense storm complex is moving through south central SD at this
hour. This complex has had a history of producing 90+ mph winds.
It will continue to move southeast over the next several hours.
The severe watch remains in effect for south central SD until 6 AM
CDT. The weather in the rest of our CWA should remain dry with
mostly clear skies through the rest of tonight. Much cooler
tomorrow with highs in the low to mid 80s across the plains and in
the 70s over the Black Hills. Another system moving through will
bring thunderstorms back into the area by the afternoon hours.
There`s some question as to how tonight`s activity will impact the
environment for tomorrow and thus where storms will develop.
Still, modest buoyancy and shear will support strong to severe
storms with large hail and damaging wind gusts.

UPDATE Issued at 440 PM MDT Tue Aug 11 2026

A Severe Thunderstorm Watch has been issued for western South
Dakota that is in effect until 8PM.

A storm developed in the northern Black Hills and moved
southeast. This storm was able to tap into the available moisture
and heat energy and grew quite large. Hail stone reports from
this storm have been upwards of 2.5 to 3.5 inches in diameter. In
addition to the large hail, locally heavy rain and gusty winds
have also been reported from these early afternoon storms.

Looking forward, there continues to be storm development in
western and northwestern SD. These storms will track east-to-
southeast through the SD plains. Strong to severe storms are still
likely with large hail and strong winds being the main concerns
but the tornado threat can`t be completely ruled out.

Stay up on the latest weather information through the evening.

&&



.DISCUSSION...(This Afternoon Through Monday)
Issued at 120 PM MDT Tue Aug 11 2026

It`s another wait and watch the sky day as more strong to severe
storms are looking likely. Latest hi res model guidance has
thunderstorm initiation happening by 2 to 4PM near the northern
Black Hills and in NW SD. As of this writing (12:30PM), clouds are
starting to bubble up over the central and northern Black Hills,
indications that the CAP is slowly being eroded away. Using the
HRRR Convective Hazard Forecast, the time frame from 4PM to 8PM
has the highest chances for severe weather in western SD, just
east of the Black Hills. From there, probabilities diminish and
track southeast to near zero by 10PM in southern SD.

When these storms get going, they are expected to track southeast
through the western SD plains. Main concerns now are large hail,
then strong winds. Isolated tornadoes can`t be ruled out at this
time.

Wednesday is the beginning of a big pattern change over the area.
Upper level high pressure will slide southeast, allowing for
moisture to flow into the area due to southwest flow. For now,
expecting clouds to build and last through Friday. So a cloudy few
days are in store. Thunderstorms are also likely tomorrow
afternoon and evening and we can`t rule out severe weather. At
the surface, moist, easterly flow north of a developing surface
low in eastern Colorado/western Kansas will allow for moderate to
strong destabilization across parts of Nebraska/southern South
Dakota. Steep mid-level lapse rates and moderate to strong
effective shear will promote supercell development from near the
Black Hills and south into Nebraska. Large hail and isolated
severe wind gusts would be possible initially.

Continued rain and storm chances last for the rest of the week
too.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Wednesday Night)
Issued At 1119 PM MDT Tue Aug 11 2026

A cluster of strong/severe thunderstorms over south-central SD
will exit the area around 12/07z. Behind it, a smattering of
IFR/MVFR CIGS may develop and persist into Wednesday morning. Low
confidence terminals will be affected so left out. More
showers/storms are expected Wednesday with local IFR conditions,
strong gusty erratic winds, and hail.

&&

.FIRE WEATHER...
Issued At 1152 AM MDT Tue Aug 11 2026

Hot and dry weather with elevated fire weather conditions
(especially over northeastern WY) will continue through today.
Cooler, unsettled, and wetter weather moves into the region
tomorrow and will last into the weekend.

&&

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

$$

UPDATE...Wong
DISCUSSION...GS
AVIATION...Helgeson
FIRE WEATHER...GS