####018010390#### FXUS63 KBIS 061537 AFDBIS Area Forecast Discussion National Weather Service Bismarck ND 937 AM CST Sat Dec 6 2025 .KEY MESSAGES... - Accumulating snow will fall across most of western and central North Dakota through this evening. There is high confidence in new snow amounts around 1 to 3 inches, and a low potential for pockets of up to 5 inches. - Another area of light snow is expected to cross the state from west to east on Sunday, with new snow accumulations from a few tenths of an inch to near 2 inches. - A more impactful system is anticipated late Monday night through Tuesday night, which may bring a period of freezing rain, accumulating snow (high chances north and east), and very strong winds to parts of western and central North Dakota. - Below average temperatures this weekend, above average for most on Monday and Tuesday, then below average favored for the rest of next week. && .UPDATE... Issued at 930 AM CST Sat Dec 6 2025 A frontogenesis heavy band of snow has setup across western and southern North Dakota. Given the 1/2 mile visibilities and the 3 to 4 hour forecast of the fgen band staying in ND, we issued a Winter Weather Advisory for snow up to 4 inches. Currently the heaviest band of snow is in Mercer county and down through the Bismarck/Mandan area. Blowing and drifting snow will also be possible statewide today. UPDATE Issued at 629 AM CST Sat Dec 6 2025 Quick update to PoPs to account for observations and trends. Snow has reached Jamestown much sooner than expected, but is struggling to commence at Bismarck despite the 12Z RAOB showing a deep layer of near-saturation with respect to ice. CAMs are not handling the coverage and placement of snow very well, and the latest HRRR and RAP are incorrectly eliminating much of the snow they are assimilating in their current conditions by forecast hour two. && .DISCUSSION... Issued at 514 AM CST Sat Dec 6 2025 Synopsis: Confidence remains high that an active northwest flow pattern will persist through late next week. Near daily shortwaves/clipper systems will bring repeated chances for accumulating snow across parts of the region. There is moderate to strong ensemble agreement on the general placement and timing of systems through Tuesday night, and that another wave is likely to follow late Wednesday/Thursday but with greater uncertainty in timing and placement. There is also high confidence that Tuesday will feature the most impactful clipper, which could produce a period of freezing rain, accumulating snow, and very strong winds (but not necessarily overlapping with the snow). Wild fluctuations in day-to-day temperatures also remain in the forecast through late next week as we alternate between periods of Arctic cold and mild Pacific air. This weekend will feature below normal temperatures with highs mostly in the single digits and teens above zero, and lows tonight around zero to 10 below. Sunday will begin to warm up in the west (especially southwest) as a warm front moves through. Above normal temperatures are then expected for Monday and especially Tuesday when areas along and to the south and west of the Missouri River could reach the 40s. The maximum and minimum NBM temperature distributions take a distinct shift colder on Wednesday, but there is very large spread (in some cases as much as 20 to 30 degrees in the 25th-75th percentile range). The following paragraphs will summarize the important forecast details for each shortwave/clipper. Today: Snow has been falling across much of northwest and north central North Dakota (except the Turtle Mountains area) since late last evening. There has also been some freezing drizzle along the I- 94 corridor from around Dickinson to Bismarck, but this threat should be waning as deeper moisture in DGZ migrates southward. The snow that has fallen thus far has been farther north than expected, but there has been a more recent trend in a southward shift. Overnight radar reflectivity across northern North Dakota has presented banding and convective signatures at times, suggesting there could be some periods of enhanced snowfall rates. This thinking is supported by RAP analysis showing 850 mb frontogenesis, steep mid to upper level lapse rates, and strong vertical lift through the DGZ. The latest RAP maintains moderate to strong low level frontogenesis through at least mid morning. Snow accumulation threshold probabilities have risen with the latest model cycle, particularly for 2 inches and above. Areas bounded by the Missouri River, Montana border, and Highway 12 have a 50 to 80 percent chance for exceeding 1 inch, a 30 to 60 percent chance for exceeding 2 inches, and a 5 to 20 percent chance for exceeding 4 inches per the experimental NBM version 5.0. These probabilities can likely be extrapolated farther north, as most 00z guidance did not pick up on the northward shift that has already been observed. Also keep in mind these probabilities are point-specific, meaning there is higher confidence in this system producing amounts this high somewhere. This leads us to advertise a broad area of 1 to 3 inches of snow through this evening, with local amounts as high as 5 inches. This also lines up well with HREF snow output. Sunday: A shortwave dragging a warm front across the state from west to east during the early morning to late afternoon is expected to bring a few hours of light to moderate snow to most locations across most of western and central North Dakota on Sunday, with the lowest probabilities again in the Turtle Mountains area. Ensemble systems project high probabilities for measurable precipitation, but only low probabilities for exceeding a tenth of an inch of liquid. Deterministic model soundings show a deep saturated layer within or just slightly warmer than the DGZ up to 700 mb, with another 100 mb layer of steep lapse rates through the DGZ placed above it. This could drive snow ratios closer to 20:1 (but elevated winds through the saturated column should discourage extremely high snow ratios). It follows that our updated snowfall forecast for Sunday is around a few tenths of an inch to near 2 inches, which is also in line with HREF output. Monday: A weak clipper is forecast to move from southern Saskatchewan through the Red River Valley during the day Monday. The Turtle Mountains area has a 30 percent chance of accumulating snow, but less than a 10 percent chance of exceeding 1 inch. The rest of western and central North Dakota is expected to remain dry through Monday evening, with milder temperatures but breezier winds. Monday night through Tuesday night: A strong Alberta clipper is forecast to cross the region over this time period. From late Monday night into Tuesday morning, the greatest concern is the potential for a period of freezing rain across western and central North Dakota. This will be dependent on whether above freezing temperatures aloft outpace those at the surface, for which there are medium probabilities. Those probabilities joined with the probability for measurable precipitation are no greater than 30 percent, but this setup seems to have the potential making of a low predictability/high impact event. The surface low is forecast to cross the state from northwest to southeast during the day Tuesday, and there is little spread in its timing and track among the 3 highest membership clusters out of 4 (composing around 85 percent of all global ensemble members). This results in high probabilities for accumulating snow along and northeast of a line from around Crosby to Jamestown, and exceedance probabilities for as high as 4 inches remain greater than 50 percent in the Turtle Mountains. The greatest overall concern with this system though is the potential for a very strong wind event, for which there is increasing ensemble confidence. Every ensemble cluster has an area of medium to high probabilities for 850 mb winds exceeding 50 kts crossing western and southern North Dakota, and recent EFI output is shifting towards higher probabilities for a high- impact event. One of the big questions is how much, if any, overlap there could be with fresh snow accumulations and the strong winds (snow that has fallen before Tuesday should not be blowable by that time). Even a slight overlap could pose significant blowing snow issues. Wednesday and beyond: There is broader ensemble agreement in yet another clipper crossing the region late Wednesday into Thursday, but with much greater uncertainty in details. The latest experimental NBM output shows a 50 to 60 percent chance for measurable snow across most of a western and central North Dakota Wednesday evening through Thursday afternoon, with a 30 to 40 percent chance of exceeding 1 inch and a 15 to 25 percent chance for exceeding 2 inches. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 629 AM CST Sat Dec 6 2025 Snow is expected across most of western and central North Dakota this morning (except areas to the north and east of KMOT), ending from northwest to southeast this afternoon and evening. Visibility under falling snow should mostly be in the IFR range, with brief periods of LIFR possible. Early morning ceilings range from LIFR in southwest North Dakota to VFR in the far north. Expect ceilings to gradually lift throughout the day, likely reaching VFR levels around the same time snow diminishes. By the end of the forecast period, another round of snow with MVFR ceilings and IFR visibility could be entering western North Dakota. Winds through this afternoon will mainly be east to northeast around 10 kts, becoming lighter and variable this evening. && .BIS WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 8 PM CST /7 PM MST/ this evening for NDZ017>020-031>036-040>047-050. && $$ UPDATE...Smith DISCUSSION...Hollan AVIATION...Hollan ####018006024#### FXUS64 KHUN 061538 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 938 AM CST Sat Dec 6 2025 ...New NEAR TERM, SHORT TERM... .KEY MESSAGES... Issued at 938 AM CST Sat Dec 6 2025 - Low to medium chances of fog tonight, with low to medium chances of freezing fog over northeast Alabama and southern middle Tennessee later tonight as temperatures drop to freezing or just below. - Low to medium (20-40%) chances of periodic light rain late Sunday afternoon through Monday morning. - Colder temperatures return early next week with sub-freezing lows Monday night, followed by a warming trend through midweek. && .NEAR TERM... (Rest of Today and Tonight) Issued at 938 AM CST Sat Dec 6 2025 A rather large upper trough spans much of the CONUS through tonight, with a shortwave ripple moving over the region through this afternoon. By this evening, zonal flow near the base of the trough will take hold over the Tennessee Valley. At the surface, a surface boundary remains over the northern Gulf, with high pressure to the north over the Tennessee Valley and up over the Appalachians. This feature will begin to gradually shift to the northeast later tonight as a cold front approaches the region. The main thing we'll be monitoring today is the low stratus cloud deck. As the previous shift mentioned, there remains uncertainty whether these clouds will break up through the day. If the clouds remain socked in, temperatures will not warm as much and lead to highs only topping out in the 40s for most locations. However, if clearing does occur this afternoon, temperatures could warm into the lower 50s. Our current forecast calls for the clouds hanging on a bit longer through the afternoon, with clouds breaking up late this afternoon through this evening. Thus, cooler high temperatures are anticipated at this time (mid to upper 40s). As for tonight, there is a low to medium chance (20-40%) of fog development. Some of this may actually be freezing fog over northeast Alabama and into southern middle Tennessee as temperatures drop to freezing or just below. Overall, expect lows in the lower to mid 30s. As clouds increase once again late tonight into Sunday and as the sun rises, any fog will then dissipate. && .SHORT TERM... (Sunday through Monday) Issued at 938 AM CST Sat Dec 6 2025 The base of the aforementioned upper trough will amplify just a bit and swing over the Southeast through Monday. Additionally, a surface cold front will traverse the region Sunday night as well, with high pressure pushing into the region from the west by Monday afternoon. With this front will come low to medium chances (20-40%) of rain for all of north Alabama and southern middle Tennessee. Thunderstorms are not anticipated with this activity due to the lack of any instability. As the front pushes to the southeast early Monday morning, rain chances will taper off. Dry conditions will then return for the afternoon. A bit warmer temperatures are expected on Sunday and Sunday night, but not by too much. Highs Sunday are forecast to only reach the lower 50s due to cloud cover, with mid 30s to around 40 degree lows Sunday night. Behind the cold front will come colder air due to cold air advection from the northwest. Highs on Monday are expected to merely top out in the lower to mid 40s. Some areas in the higher terrain of northeast Alabama and southern middle Tennessee may see cooler highs, in the upper 30s to around 40 degrees. && .LONG TERM... (Monday night through Friday) Issued at 1105 PM CST Fri Dec 5 2025 Back to sub-freezing lows again Monday night with clear skies and high pressure building in. Lows in the mid 20s are expected. This intrusion of colder air should be brief, as warm air advection ahead of another front moving through the western Great Lakes early next week keeps things on the warmer side. Highs in the lower 50s should warm into the 55 to 60 degree range on Wednesday with lows warming as well into the lower to mid 30s. This front seems to have a hard time pushing into the southeast and hangs up over eastern Texas into the Ohio Valley. However, a weak pre-frontal trough axis looks to be close enough to produce a few showers over the area Wednesday night into Thursday. This weak pre-frontal trough axis may focus a bit more moisture and forcing over the area Thursday afternoon into Thursday night, before pushing east of the area. This should pull the precipitation east with it as colder and drier air moves into the area. Highs look to drop back down into the upper 30s to lower 40s again on Saturday. && .AVIATION... (12Z TAFS) Issued at 549 AM CST Sat Dec 6 2025 IFR-level stratus continues to blanket the entire forecast area this morning, but very low chances for light rain will remain well south of the terminals and a light westerly flow has thus far inhibited development of BR/FG. There remains a considerable amount of uncertainty regarding when the stratus layer will eventually begin to mix out (if it does so at all), but at this point we have optimistically indicated a temporary return to VFR conditions this evening. However, with minor low-level moisture advection expected to begin ahead of a secondary cold front, there is some concern that low stratus (and perhaps some mist/drizzle) may begin to redevelop prior to 12Z Sunday, with either no (or only a brief) opportunity for clearing this evening. Sfc winds will remain light for the duration of the TAF period, with winds shifting to SSE by late mid/late aftn. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...None. TN...None. && $$ NEAR TERM...26 SHORT TERM....26 LONG TERM....KTW AVIATION...70/DD