FXUS65 KTFX 151947 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 147 PM MDT Tue Oct 15 2024 .SYNOPSIS... Changes will be coming to the Northern Rockies from Wednesday evening and through the night as a Pacific cold front brings colder temperatures to all location, in addition to accumulating snow to the mountains of Southwest Montana. One more day of above normal temperatures is expected during the day on Wednesday prior to the front, in addition breezy and gusty south to west winds. && .DISCUSSION... Rest of today through Wednesday...H500 ridge axis will continue to shift east of the Northern Rockies through tonight as longwave troughing digs south and east from the Gulf of Alaska towards the Pacific Northwest. By Wednesday morning the upper level ridge axis will be over the Northern and Central Plains, with increasing southwest flow over the Northern Rockies ahead of the digging longwave trough. This southwesterly flow combined with warm air advection will translate to one more day of above normal temperatures across all of Southwest through North Central Montana, with breezy and gusty south to west surface winds across most lower elevations. Winds will be especially gusty in the north-south orientated valleys of Southwest Montana and along the Rocky Mountain Front on Wednesday, with the latest NBM probabilities suggesting a 30-80% chance of wind gusts exceeding 45 mph here. High temperatures on Wednesday will reach the mid-60s to near 80s degrees before a strong Pacific cold front sweeps east and across Southwest through North Central Montana Wednesday evening/night. As the Pacific front sweeps east across the CWA Wednesday evening/night winds will increase further ahead of and behinds the frontal passage across all locations, with widespread gusts of 35-45 mph. BUFKIT soundings along the Rocky Mountain Front from Wednesday evening through the overnight hours do support the potential for mountain wave activity that could lead to wind gusts in excess of 60 mph over portions of the East Glacier Park Region, Northern High Plains, and Eastern Glacier/Western Toole/Central Pondera Counties; however, NBM probabilities for wind gusts in excess of 60 mph are less supportive and only around a 30-40% chance. Thursday through Friday...will be the most impactful portion of the forecast period, with temperatures falling below to well below normal (especially in Southwest Montana) and accumulating mountain snow occurring across the mountains of Southwest Montana as the longwave trough and associated closed low digs southeast from the Pacific Northwest to over the Desert Southwest. Snow levels early Thursday morning of 4000 feet (North Central Montana) to 7000 feet (Southwest Montana) will fall precipitously through Thursday afternoon, especially across Southwest Montana where periods of moderate to heavy precipitation will promote dynamic cooling. These lowering snow levels and periods of heavier precipitation will lead to rain quickly changing to snow in the mountains of Southwest Montana through Thursday morning, most notably in the Tobacco Root Mountains and Gallatin, Gravelly, and Madison Ranges. The Winter Storm Watch for the Gallatin and Madison County Mountains and Centennial Mountains has been upgraded to a Winter Storm Warning as NBM probabilities for 12" of snow within the aforementioned mountains have a 50-90% chance of occurring (generally above 7000 feet), which combined with ongoing outdoor recreation (i.e. hunting) has a high likelihood of leading to moderate to major impacts. In addition to the Winter Storm Warning, a Winter Weather Advisory has been issued for the Big Belt, Bridger and Castle Mountains given the expected impacts to travel over Bozeman Pass, especially during the Thursday evening commute when a quick 1-3" is expected to occur. Snow will gradually taper off Friday morning through the early afternoon as the upper level disturbance sags south of the Northern and Central Rockies. - Moldan Saturday through Tuesday...Weak upper level ridging will try to develop over MT over the weekend. By Tuesday, an upper level trof will start to move over MT. Expect slightly warmer temperatures over the weekend, but as the next trof approaches by Tuesday, temperatures will cool back down. The system for next week does not look quite as strong as it did a few days ago, thus precipitation amounts are looking to be on the light side at this time for Mon/Tue. Brusda && .AVIATION... 15/18Z TAF Period VFR conditions will prevail at all terminals except for the KEKS terminal during this TAF period. At the KEKS terminal smoke and haze from a wildfire has been intermittently reducing visibility to MVFR levels and will continue to do so through at least 15/22Z. During the beginning of this TAF period smoke and haze will be along and south of the KGTF terminal. Winds will be mostly light and variable across all terminals excluding the KEKS terminal during the majority of this TAF period until the last couple of hours. This is due to winds increasing due to a cold front beginning to move near Montana by the end of this TAF period. At the KEKS terminal winds will increase from 16/00Z through the end of the TAF period and gust up to 31 kts by the end of the TAF period. There will be intermittent mountain obscuration in Southwestern Montana through 00Z due to smoke and haze. -IG Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PRELIMINARY POINT TEMPS/POPS... GTF 48 75 40 54 / 0 10 50 10 CTB 44 65 35 53 / 0 10 20 10 HLN 41 74 38 50 / 0 10 70 50 BZN 42 78 35 46 / 0 0 80 80 WYS 27 67 28 42 / 0 0 100 100 DLN 40 73 35 46 / 0 10 80 70 HVR 43 75 41 60 / 0 0 30 10 LWT 50 78 39 51 / 0 0 40 60 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 3 AM Thursday to noon MDT Friday for Big Belt, Bridger and Castle Mountains. Winter Storm Warning from 3 AM Thursday to noon MDT Friday for Gallatin and Madison County Mountains and Centennial Mountains. && $$ http://www.weather.gov/greatfalls