FXUS63 KUNR 211128

AFDUNR



Area Forecast Discussion For Western SD and Northeastern WY

National Weather Service Rapid City SD

528 AM MDT Mon Sep 21 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 12Z TAFS Through 12Z Tuesday Morning)

Issued At 526 AM MDT Mon Sep 21 2026



Areas of low clouds and fog will persist across the area this

morning with IFR/LIFR conditions. Some visibility improvement is

expected later this morning, however, stratus will linger withMVFR/IFR conditions through the forecast period.



&&



.UNR WATCHES/WARNINGS/ADVISORIES...

SD...None.

WY...None.

&&



$$



UPDATE...GS

DISCUSSION...MLS

AVIATION...SE