766
FXUS63 KUNR 210428
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1028 PM MDT Sun Sep 20 2026

.KEY MESSAGES...

- Showers will continue to gradually decrease in coverage tonight.

- Areas of fog will continue through Monday morning. Reduced
  visibilty is expected around the Black Hills and across the
  western South Dakota plains for the Monday morning commute.

- More clouds than sun to start the week, followed by warmer and
  drier conditions later in the week.

&&

.UPDATE...
Issued at 935 PM MDT Sun Sep 20 2026

Showers, low clouds, and fog are the big stories for the
overnight hours.

The latest upper level low is still spinning and tracking
eastward through the central states. This low has been bringing,
and will continue to bring, bands of rain showers, drizzle, and
low clouds to the area. Slowly, the rain showers will improve
overnight but the drizzle and low clouds will last well into
tomorrow/Monday.

The other challenge for tonight and tomorrow is the fog. Easterly
winds will keep patchy fog and low visibility in and around the
Black Hills and SD plains through tonight and into tomorrow. Some
hi-res models keep fog in the SD plains through Monday afternoon.
So there is some evidence that the fog, or low clouds, will linger
through most of Monday.

&&

.DISCUSSION...(This Afternoon Through Saturday)
Issued at 1144 AM MDT Sun Sep 20 2026

Water vapor and upper level analysis depicts a low centered over
Wyoming, a ridge extending up the West Coast, and another low just
off-shore of California. At the surface, the low is over the western
Nebraska Panhandle with a weak trough extending northwestward along
the Bighorns. Latest radar imagery has a large swath of rain over
the western and central South Dakota plains, rotating counter-
clockwise around the upper low.

For the rest of today, the main band of rain over the South Dakota
plains will continue to lift northward, being replaced by a few
smaller, less organized showers for the afternoon and evening hours.
Rain showers across northeastern Wyoming will be less, as drier gets
pulled up from southeastern Wyoming. High temperatures will remain
cool with the damp conditions and abundant cloud cover, with no
deviation from blended guidance which is close to current temps.

The upper low opens up and drifts east overnight, which will in-turn
ends the rain showers from west to east. Lingering moisture in the
air, combined with surface pressure rises and light winds, will
result in areas of fog and low clouds into Monday morning.
Visibility will gradually improve late Monday morning, with the
lower ceilings and clouds sticking around throughout the day.

More clouds and some fog for MOnday night/Tuesday across the South
Dakota Plains and the southern Black Hills - with the Northern Black
Hills and portions of northeastern Wyoming becoming sunny. Clouds
will gradually decrease across the entire area through the day, with
increasing south-southeasterly winds. The strongest winds, 15 to 25
mph, will likely be across northwestern South Dakota where the
pressure gradient looks to be the tightest.

A weak shortwave trough moves through Wednesday and Wednesday night,
which could result in some showers across the area. The wave moves
through fairly quickly, thus, some areas should remain dry.

A drier, warmer pattern then sets up for the end of the week into
the weekend, with highs about 5 to 10 degrees above average.

&&

.AVIATION...(For the 06Z TAFS Through 06Z Monday Night)
Issued At 1028 PM MDT Sun Sep 20 2026

Areas of light rain will accompany widespread IFR/LIFR CIGS and
areas of MVFR/IFR VSBY (BR/FG) late tonight through Monday
morning. Some gradual improvement is expected late Monday morning
through the afternoon as fog dissipates, but MVFR/IFR CIGS are
expected to linger through the rest of the forecast period
(especially the Black Hills area). Light showers may also develop
Monday afternoon, which could reduce VSBY to MVFR/IFR at times.

&&

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

$$

UPDATE...GS
DISCUSSION...MLS
AVIATION...13