FXUS63 KBIS 050408 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 1008 PM CST Wed Dec 4 2024 .KEY MESSAGES... - A cold night is on tap tonight with wind chills down to 25 below zero. Temperatures will then increase through the weekend. - Mainly dry conditions are expected Thursday through Saturday, with widespread low to medium chances (20 to 60 percent) for precipitation returning Sunday into early next week. && .UPDATE... Issued at 1001 PM CST Wed Dec 4 2024 Quiet weather remains over the area, though a little light snow still looks like it could develop later tonight over southwest North Dakota. Chances are low (20 percent), and any accumulation would be minimal at best. UPDATE Issued at 647 PM CST Wed Dec 4 2024 Winds continue to gradually diminish, and with that the end of almost all blowing snow with only some patchy spots around the Turtle Mountains. Therefore, have let Winter Weather Advisory expire. Other than that, other change was for later tonight adding some low snow chances over the southwest as a modest short wave drops through and mid-level warm air advection starts to develop. UPDATE Issued at 429 PM CST Wed Dec 4 2024 Have trimmed off another tier of counties on the western edge of the Winter Weather Advisory, as winds have diminished some over this area. With that said, can not rule out a little drifting snow in spots as winds continue to gust in the 30 to 35 mph range, but the threat for blowing snow has diminished. && .DISCUSSION... Issued at 202 PM CST Wed Dec 4 2024 Our main concern early on is the ongoing winter weather advisory in effect until 6 PM for the Turtle Mountains area into the James River Valley. Latest observations have shown some improvement in visibilities compared to this morning. However, we are still into the wind advisory criteria and certainly not cancel a winter weather advisory and issue a wind advisory for only a few hours. Most likely will let the advisory ride through the afternoon. The next shift would be able to cancel early if warranted. If we would do any cancellations, it would again be the western tier counties. Next in line is wind chill temperatures tonight and overnight lows early Thursday morning. Wind chills currently bottom out around 25 below zero, which if this verifies, would be below Cold Advisory criteria. Forecast lows early Thursday morning are expected to drop below zero for many areas in northern and eastern portions of the forecast area. The surface high pressure center behind the exiting clipper system is quick moving but does propagate southeast across the forecast area tonight and at 12 UTC Thursday is forecast to be roughly along the ND/SD border between Bismarck and Aberdeen. This is an excellent location for cold low temperatures over south central ND, including Bismarck. A look at the RAP moisture profiles shows there may be some lingering low level stratus over eastern ND and possibly into the James River Valley. Mid level moisture (700mb) has pushed into western ND, approaching the Missouri River. There may be a short window around 12 UTC, where temperatures would be able to bottom out. This is roughly along and just east of the Highway 83 corridor. A fresh and plentiful snowpack would have really helped temperatures bottom out, but the warm temperatures yesterday ate up a lot of our latest fresh snow. Still think there is enough of a snowpack to help a little. How quickly and efficiently the low clouds exit to the east and how quickly the mid clouds approach from the west will be the determining factor. We did use a blend of some of the cooler guidance to lower temperatures a bit over central ND. The approaching mid clouds from the west is due to a southerly return flow and warm advection on the back side of the Arctic High. Latest NBM guidance has backed off a bit with the PoPs over western and into south central ND. Will keep some slight chance pops for consistency but overall, the threat for snow amounts greater than a trace to a few tenths seems limited. The latest NBM probabilities of 24 snow amounts of a tenth of an inch or more, ending at 18Z Thursday are highest over west central into southwest ND and max out only around 30 percent. Although we start off cold on Thursday morning, and we will likely remain mostly in the teens over eastern portions of central ND, the western half of ND is forecast to see high temperatures climb into the 20s with some mid and even upper 30s possible in the far southwest. We remain in a northwest upper air pattern late in the work week and into the weekend. Strong west coast upper level ridging will result in building heights pushing into the northern Plains. This will push most of the waves propagating through the upper level ridge to the north and east of the forecast area. In addition, NBM ensemble temperatures indicate rather significant warm-up over the forecast area, from Thursday through Saturday. Although these is some spread, in both the forecast highs and lows, it's not all that large (5 to 7 degrees). Currently it looks like a nice period of moderating temperatures and mostly precipitation free, from Thursday through Saturday. It may be a little breezy on Saturday, but our current forecast high temperatures range form the mid 30s around the Turtle Mountains, to the middle 50s in the southwest. We do see increasing ensemble spread Sunday and early next week as the western North America ridge breaks down, at least temporarily. A northeast Pacific upper low moves onshore and brings widespread low to medium (30% to 60%) chances of precipitation to all of western and central ND (based on the latest NBM guidance). Currently, although the precipitation looks to be widespread across the forecast area in the late Sunday through early Tuesday timeframe, the latest long range ensemble guidance is indicating mainly light precipitation amounts. The probability of over an inch of snow in a 24 hour period is maxed out at around 25 to 35 percent. We'll see if this changes as head into the upcoming weekend. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 1001 PM CST Wed Dec 4 2024 Mainly quiet weather is expected, though localized light snow may develop late tonight over southwest North Dakota. This may result in a spot or two of MVFR visibility, but overall most locations should remain VFR. && .BIS WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...JJS DISCUSSION...TWH AVIATION...JJS