990 FXUS63 KUNR 110535 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 1035 PM MST Sat Mar 10 2018 .DISCUSSION...(This Evening Through Saturday) Issued at 250 PM MST Sat Mar 10 2018 Current surface analysis shows low pressure over southeast NE, with cold front well south and east of the area. Upper level analysis shows compact upper low now over far north central NE, moving southeastward. Northwest winds gusting as high as 45 to 50 mph persist across the northwest and west central SD plains. KUDX radar shows areas of snow mainly east of the Black Hills. Convective rain and snow showers have also developed over far southwest SD in area of leeside convergence. Some clearing has developed on the back side of the system over northeast WY. Temps currently range from the mid to upper 20s over northeast WY and northwest SD to around 40 across far southern SD. The combination of snow and wind over much of northwest SD continues to produce greatly reduced visibilities in some areas. Snowfall amounts of 1 to 2 inches have been common across most of northwest SD, locally higher toward the ND border. Conditions will improve from northwest to southeast across the area late this afternoon and evening as the system moves further southeast away from the area. Winds will begin to decrease toward sunset and continue to diminish tonight. The bulk of snowfall this evening will be across south central SD on the back side of the system, where an inch or so of accumulation is possible before the snow moves out of the region. Lows tonight will be on the chilly side, mostly in the teens to around 20, with some single digits in sheltered areas of northeast WY and far western SD. Added some patchy fog to far northeast WY and parts of northwest SD late tonight/early Sunday. Dry, but cool, conditions will return for Sunday and the first part of the week as shortwave ridge passes quickly over the area. Highs will be near to slightly below average Sunday and Monday, 30s and 40s, warmest over northeast WY. A stronger ridge will build over the western US Tuesday and move east into the plains midweek. This will bring much milder air into the region, especially Wednesday and Thursday. Some 60s can be expected from southern parts of northeast WY into southwest SD, with 70 certainly possible in a few spots. Snowpack will limit temp potential over much of northwest SD, highs expected to mostly be in the 40s to lower 50s Wednesday and Thursday. As ridge shifts east of the region late in the week, a large scale trough will push into the western states, bringing a more unsettled pattern into next weekend. A northern stream shortwave should bring a cold front across the area Thursday night into Friday, with a chance for rain and snow. Medium range models are inconsistent on evolution of the trough to the west and its impact on our area next weekend, but colder and occasionally unsettled weather is looking increasingly likely. && .AVIATION...(For the 18Z TAFS Through 18Z Sunday) Issued At 1007 AM MST Sat Mar 10 2018 A quick moving disturbance has resulted in areas of snow across northwestern South Dakota through central South Dakota and parts of northwestern Wyoming today. MVFR/IFR conditions are expected with the snow. Snow will quickly taper off at KGCC after 20z with gradual improvement to VFR conditions. Elsewhere, snow will taper off later this evening across much of the area with improvements to VFR conditions tonight into Sunday morning. In addition to the snow, strong NW winds of 20 to 35 knots with gusts to 45 knots are expected today before weakening Sunday. && .AVIATION...(For the 06Z TAFS Through 06Z Sunday Night) Issued At 1032 PM MST Sat Mar 10 2018 MVFR CIGS will continue across much of the western SD plains tonight before pushing east of the area. Patchy fog may develop across portions of northeast Wyoming and northwest South Dakota. VFR conditions are expected for much of the day Sunday. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ DISCUSSION...26 AVIATION...13