956
FXUS63 KUNR 201122
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
522 AM MDT Sun Sep 20 2026

.KEY MESSAGES...

- Risk for excessive rainfall lingers through Sunday across
  eastern Wyoming into western South Dakota.

- Areas of fog possible again Sunday morning across much of
  western South Dakota.

- Gradual warming with drier conditions next week.

&&

.UPDATE...
Issued at 1020 PM MDT Sat Sep 19 2026

Scattered thunderstorms have dotted the landscape this Saturday
evening. Heavy rain has been the big talking point from these
storms. While most stations have reported a range of few
hundredths of an inch to to around a quarter inch of rain, a few
isolated stations reported an inch of rain out of the heavier
storm cells. More reports likely Sunday morning.

Looking ahead to Sunday, no changes were made to the inherited
forecast. Still expecting the upper level closed low to track
eastward over the CWA. As it approaches, more showers will develop
on the front side of the low Saturday night with lingering precip
lasting through Sunday night.

Severe weather (hail & wind) is not expected but flooding due to
heavy rain can`t be ruled out, especially in the areas that see
training storms and/or heavy rain.

&&

.DISCUSSION...(This Evening Through Saturday)
Issued at 122 PM MDT Sat Sep 19 2026

Current analysis shows the closed low continuing to spin and move
slowly east into western Wyoming this afternoon. Downstream of
this area of low pressure much of eastern Wyoming and western
South Dakota sit under weak flow and widespread low clouds. These
clouds have allowed the temperatures to remain steady, not
changing much from the overnight low temperatures as most areas
are still sitting in the low 60s with a few pockets of mid to
upper 60s.

Heading through the rest of today, we will watch the Black Hills
and areas to the west and south for potential thunderstorm
initiation this afternoon ahead of the main area of low pressure
as it will continue to move east toward eastern Wyoming. Limited
heating today may suppress more robust thunderstorm cores from
developing today but we are still expecting some thunderstorms to
develop as the better dynamics associated with the main area of
low pressure continues to approach the area. Window for initiation
looks to be now (1pm MDT) through the next hour or so. The
coverage and strength of the thunderstorms will alter both the
marginal severe risk and excessive rainfall risk at least through
Saturday. Still any storm that does develop will produce moderate
to rainfall as they will be slow moving and will be able to tap
into the modest PWAT values sitting across western SD.

Come Sunday we expect the coverage of showers with embedded
thunderstorms to increase as the area of low pressure moves into
the region. Nearly everyone should see rainfall but totals will
depend on your proximity to the axis of where the clustering of
thunderstorms are expected to be. Probabilities continue to  of
seeing rainfall amounts over 1" over the Black Hills and adjacent
areas. Outside of these areas we could still rainfall totals close
to 0.50". Sunday will begin cloudy and foggy in most areas with
mist/drizzle occurring before transitioning into rain. This rain
will persist through much of the day before we begin to slowly dry
out from west to east come Sunday night before we finally get rid
of the unsettled weather by Monday. This will begin the gradual
warm and dry pattern that will develop as a ridge of high pressure
begins to expand across the Intermountain West. Temperatures will
climb back to or slightly over seasonal normals by Wednesday.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Monday Morning)
Issued At 521 AM MDT Sun Sep 20 2026

Showers and thunderstorms will continue across the area through
Sunday night. Widespread IFR conditions are expected...even LIFR
across parts of western SD, especially the Black Hills area.

&&

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

$$

UPDATE...GS
DISCUSSION...Woodward
AVIATION...SE