902 FXUS63 KUNR 300930 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 230 AM MST Fri Dec 30 2022 .DISCUSSION...(Today Through Thursday) Issued at 230 AM MST Fri Dec 30 2022 Current surface analysis shows nearly stationary frontal boundary from eastern MT and northwest SD to south central SD and eastern NE. Upper level analysis shows near zonal flow from the northern Rockies through the northern Plains. Skies are mainly clear across much of the forecast area now, with lingering clouds over far eastern portions of the area decreasing. Patchy fog could develop early this morning along and to the northeast of the boundary as skies clear. Temps are mostly in the 20s and lower 30s with relatively light winds. Mostly quiet weather is expected over the next couple of days to end the year. Temps will be slightly above average levels, with highs mostly in the mid 30s to mid 40s each day, a bit cooler over far northwest SD today. South to southwest winds will become breezy today from northeast WY to southern SD, especially over southern Campbell County, where some gusts to over 40 mph are expected by the afternoon. There could be some fog again late tonight/early Saturday over far eastern areas. A weak disturbance could also bring a bit of light snow/flurries late tonight into Saturday from parts of northeast WY to the Black Hills and far southwest SD, but little in the way of accumulation is likely for most areas. Attention for the beginning of 2023 turns to an upper trough that is still well off the west coast at this time, but will move quickly onto the west coast Saturday and across the western US later in the weekend. Eventually this system will make it into the Plains for the beginning of next week. There are still a lot of differences between the various models on the track and even the timing as it moves across the Plains. Latest ensemble output, especially the GEFS, show a wide variety of solutions Sunday and Monday as the system pushes into and through the region. The EC continues to be the farthest south solution and has probably been the most consistent model from run to run. GEFS is farthest north with its mean track, but has started to shift a bit more south over the last 2 to 3 runs. Canadian output has taken a noticeable shift farther south over the last couple of runs, closer to the EC now. 00z NAM shows a farther north track like the GFS at this point. The differences seem to mostly be due to how far south the system may dig as it comes across the southwest US this weekend and also how a northern stream wave moving across southwestern Canada into the northern Plains interacts with the system as it moves into the Plains at the beginning of the week. It will likely be at least another day before models start to come into a better consensus on things, especially with regard to snowfall and impacts for our area. However, it is starting to look more likely that the bigger impacts with regard to snowfall would be across southern portions of the forecast area, potentially near and south of I-90, but especially across far southern SD where there is anywhere from a 30 to over 70 percent probability right now for 6 inches or more of snow, depending on the model. It still looks like winds will not be a big factor with this system, but there could still be enough across parts of the SD plains to cause minor blowing/drifting of any snow later Monday into Tuesday. Winter storm watches could be issued later today or tonight for at least parts of the forecast area for the late weekend/early week period if heavier snow potential persists or increases. The system should move quickly east-northeast of the region Tuesday, with improving conditions in most areas. Upper high moving across the region from the northwest during midweek should bring dry conditions into late week. Temps will likely be slightly below average Monday through Wednesday, with near or slightly above average temps toward the end of the week. && .AVIATION...(For the 06Z TAFS Through 06Z Friday Night) Issued At 1003 PM MST Thu Dec 29 2022 Some fog with local IFR/LIFR conditions is possible late tonight/early Friday towards central South Dakota. Otherwise, VFR conditions expected through the TAF period. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ DISCUSSION...26 AVIATION...7