FXUS65 KTFX 040424 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 924 PM MST Tue Dec 3 2024 Aviation Section Updated. .KEY MESSAGES... - Slightly cooler temperatures on Wednesday over the plains in wake of a weak cold front, with below normal temperatures linger in the Milk and Missouri River Valleys on Thursday. - High temperatures on Saturday will be 10 to 20 degrees above normal across all of Southwest through North Central Montana. - Predominately dry conditions are expected through the remainder of the work week; however a few light rain/snow showers can't be ruled out on Wednesday across Hill and Blaine Counties. - Wind begin to increase from Thursday through Friday along the Rocky Mountain Front, peaking over the weekend. - Better chances for widespread precipitation return this weekend. && .UPDATE... /Issued 843 PM MST Tue Dec 3 2024/ Satellite imagery this evening shows high clouds streaming across north-central and southwest MT in northwest flow aloft downstream of an upper level ridge centered across the Pacific NW. At the surface, winds are relatively light across most of the area with the exception of locations along the immediate east slopes of the Rocky Mtn Front. With primarily thin cloud-cover, cannot rule out some patchy fog development across portions of mainly Hill, Blaine and Chouteau counties while quiet conditions prevail otherwise through tonight. Hoenisch && .DISCUSSION... /Issued 843 PM MST Tue Dec 3 2024/ - Meteorological Overview: H500 ridging over the western seaboard will gradually shift eastward towards the Northern Rockies, with the ridge axis moving over the region on Friday. As the ridge shifts eastward several weak shortwaves will crest the ridge and dive southeast and over the Northern Rockies. These shortwaves will be largely robbed of moisture and predominately lead to periods of increased cloud cover; however, and isolated rain/snow shower can't be ruled out over extreme northeastern portions of North Central Montana (i.e. northeast of a Lewistown to Chester line) on Wednesday and then over the Continental Divide on Friday. By Saturday a potent shortwave over the Gulf of Alaska will breakdown the H500 ridge over the Western CONUS/Canada, with this shortwave moving over the Northern Rockies during the day on Sunday and northerly flow remaining in place over the region through early next work week. The breakdown of the ridge will lead to a period, potentially 24-36 hours, of strong to High Winds, especially along the Rocky Mountain Front. Additionally, this shortwave will bring increasing chances for widespread precipitation to most of Southwest through North Central Montana, with the best chances occurring in the mountains. - Moldan - Forecast Confidence & Scenarios: Winds : Although breezy conditions are generally expected for much of the week, the strongest and most widespread winds hold off until the weekend. Winds initially strengthen again along the Rocky Mountain Front Thursday night amid a tightening pressure gradient for more of a 'run of the mill' event before the potentially higher impact winds move in late Friday through early Sunday. Around 55% of the (values in parenthesis) ensembles now favor a vigorous trough diving into the Northern Rockies this weekend, though there are slight timing differences among the supporting members. Climate anomaly indicators such as the NAEFS and the EC EFI are now picking up a signal for a stronger end wind event, with NAEFS H850-700 wind speeds now forecasted to approach 2 standard deviations above normal and EFI value of 0.5 to 0.7, and even a shift of tails of 0, residing along and in lee of the Continental Divide. NBM probabilities for wind gusts in excess of 55 mph continue to increase from late Friday through Saturday, with areas like Cut Bank, Browning, and East Glacier now possessing a 50% and 80%, 80% and 90%, and 70% and 90% chance respectively. - RCG/Moldan Snow this weekend into Monday: More seasonable temperatures and accumulating snow potential are expected to follow the winds Sunday into Monday. Most ensemble members continue to forecast H700 temperatures potentially falling to around -15C Sunday night into early Monday for at least some light snow at all elevations, particularly the northerly upslope areas Central/North-central and Southwest MT. Overall, mountain areas are favored for the higher amounts. Of course this will all depend on the 55% chance that the trough will be deep and cold enough to materialize this scenario. Temperatures : Temperatures will overall be warming well above average through Saturday, though the colder air will linger in the river valleys of Hill, Blaine, and Chouteau counties through Thursday. I lowered temperatures toward the Canadian models in these areas to account for slow warming today and the cold front moving in later today into Wednesday. - RCG && .AVIATION... 04/06Z TAF Period VFR conditions prevail at area terminals through tonight under a northwest flow aloft with some thin high level clouds streaming across the region. Surface winds will remain somewhat variable across the plains overnight with a wind shift to the north and northeast moving south across the N-central MT plains Wednesday morning. Low clouds are likely to spread south into the KHVR and KCTB areas with the wind shift Wednesday morning with potential for a period of MVFR ceilings. Hoenisch Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PRELIMINARY POINT TEMPS/POPS... GTF 22 40 19 48 / 0 0 0 0 CTB 17 31 19 40 / 0 0 0 0 HLN 26 46 23 48 / 0 0 0 0 BZN 21 46 18 47 / 0 0 0 0 WYS 8 38 6 38 / 0 0 0 0 DLN 23 46 18 45 / 0 0 0 0 HVR 14 26 11 33 / 0 10 10 0 LWT 25 42 22 50 / 0 10 0 0 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls