FXUS63 KUNR 020512 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 1012 PM MST Sun Feb 1 2026 .KEY MESSAGES... - Patchy dense fog will develop across western SD tonight. - Breezy northwest winds across northwestern and southwestern SD Monday - Above average temperatures and mostly dry weather through next week && .DISCUSSION...(This Evening Through Sunday) Issued at 115 PM MST Sun Feb 1 2026 Some sunshine is filtering through mid- and high-level stratus over most of the area this afternoon. Far eastern reaches of the area have dealt with a thicker and lower cloud deck. A back- door cold front is draped across the SD plains, coming to rest against the eastern elevations of the Black Hills. West of the boundary, a few locations have snuck up to 50F. .TONIGHT... A mesoscale surface high settles into western South Dakota overnight, backing the northerly winds and making them easterly. Though relatively light, they should be enough to produce some patchy fog as the moist boundary layer is subjected to widespread orographic lift. Greatest threat for the patchy fog will be west of the Missouri River but east of the Black Hills and east of a line from Buffalo, SD to Pine Ridge, SD. Current HREF probabilities suggest about a 50% probability of visibilities less than a mile and about a 35% chance of visibility slipping under 1/2 mile in this same area. Fog development looks likely (90%+). Low temps will range from the low 30s in northeast Wyoming to low 20s in south-central South Dakota. .MONDAY... Breezy winds may be the most consequential weather on Monday with northwestern South Dakota experiencing wind gusts of up to 35-45mph as another mid-level shortwave traverses the area. The northwest flow of the polar jet will push the vorticity lobe of the shortwave through central South Dakota by sunset. AM showers of rain/snow are possible in eastern Montana / western North Dakota before crossing into central/eastern South Dakota in the evening. Have maintained some 20% PoPs on the eastern fringe of the forecast area for Monday eve. Were the precip to fall, some raindrops could be mixed in with the flakes. No accumulation is anticipated. .TUESDAY... The busy northwesterly flow at H5 continues. The active pattern brings a cold front dashing through the area on Tuesday afternoon/evening. Ahead of the front, expect highs to plateau in the 40s. The strong northwesterly winds behind the front should be enough to produce some upslope snow in the Black Hills. Current guidance suggests a reasonable 1-3" with a rain/snow mix in the foothills and surrounding plains. .SECOND HALF OF THE WEEK... Currently Wednesday and the remainder of the forecast is dry and mild. Temps will generally be about 20 degrees warmer than seasonal norms. Thursday brings the week's warmest temps with the negatively tilted *ridge* overrunning this CWA. Highs in the 60s should threaten some warm high records and warm min temp records are also in danger. Confidence in the extended forecast is lower than normal due to the proximity of the polar jet and its attendant baroclinic zone in eastern South Dakota. Any unforeseen wiggle of the jet could bring drastic changes in the temperature forecast. That's the bad news. The good news is that the GFS, outlier as it was, has backed away from it's cold solution for next week. && .AVIATION...(For the 06Z TAFS Through 06Z Monday Night) Issued At 1010 PM MST Sun Feb 1 2026 Patchy fog and low clouds are expected to develop across the NW SD plains after 06Z, resulting in localized MVFR-IFR cigs/vsbys. Otherwise, VFR conds are expected throughout the TAF period with gusty northwest winds developing Monday afternoon. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ DISCUSSION/KEY MESSAGES...Nicolaisen AVIATION...JC