349 FXUS63 KUNR 132309 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 409 PM MST Mon Jan 13 2025 .KEY MESSAGES... - Light snow tonight and Tuesday with the highest accumulations over the northern Black Hills - Warmer mid-week - Arctic air this weekend into early next week && .DISCUSSION...(This Evening Through Monday) Issued at 154 PM MST Mon Jan 13 2025 The upper low, and associated surface low, has dropped southward into northern Minnesota this afternoon and is currently swinging an upper trough across the Dakotas producing areas of light snow. A couple more disturbances will cross the forecast area tonight into Tuesday with each one bringing weak QG/frontogenetic forcing, particularly along the stationary boundary in place along the eastern parts of the forecast area. Deep layer moisture is limited, however could see 1 to locally 2 inches of snow on the plains tonight through Tuesday morning. Boundary layer flow generally supports Froude numbers >1 and 0-2km RH >90% over the northern Black Hills until around 18z Tuesday. HREF has 60% chance >0.40" QPF over the highest elevations of the Black Hills and 70-90% chance 0.25" QPF. Looks like a good recipe for 4-8" of snow. Bufkit soundings depict a bit more westerly component to the wind than is usual in upslope snow events, so the highest total snow accumulations are expected to be displaced more toward the western edge of the hills, between Cheyenne Crossing, Buckhorn, and Moskee. A Winter Weather Advisory remains in effect over the northern Black Hills. For Wednesday and Thursday, an east-west oriented upper ridge will flop southward across the northern plains. A surface warm front will promote warming westerly downslope flow. Milder temperatures will develop, particularly on the eastern slopes of the Black Hills and the adjacent plains, where high temperatures around 50F area possible, per ensemble guidance. For the coming weekend, confidence is high that a deep upper trough will drop southward over the eastern 3/4ths of North America opening the door for arctic air to spill into the northern Plains. Some light snow will occur. Temperatures will be 20-30F colder than average but the coldest air will be east of the CWA. Apparent temperatures may be cold enough for the issuance of Extreme Cold products, but right now, record-breaking cold is not anticipated per EFI/NBM guidance. && .AVIATION...(For the 00Z TAFS Through 00Z Tuesday Evening) Issued At 405 PM MST Mon Jan 13 2025 MVFR/IFR ceilings with some light snow/flurries will persist across the plains of western South Dakota from far northwestern South Dakota into south central South Dakota. KRAP terminal may see brief period of MVFR ceilings through early evening, but confidence is low. MVFR/IFR conditions with snow will also continue for the northern Black Hills through Tuesday morning. A brief period of light snow is possible over northeastern Wyoming tonight, impacting the KGCC terminal. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...Winter Weather Advisory until 11 AM MST Tuesday for SDZ024. WY...Winter Weather Advisory until 11 AM MST Tuesday for WYZ057. && $$ DISCUSSION/KEY MESSAGES...10 AVIATION...7