125 FXUS65 KTFX 190944 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 344 AM MDT Thu Sep 19 2019 .SYNOPSIS... A strong upper level disturbance moving across the Great Basin and Central Rockies today through Friday will bring increasing chances for precipitation to Southwest and Central Montana to end the work week. Temperatures over Southwest will cool enough to allow for a rain snow mix as low as 6500 feet tonight through Friday night, with accumulating snow expected above 8000 feet. && .Early Morning Update... Issued a Winter Weather Advisory for elevations above 8000ft in Madison and Gallatin Counties for the potential impacts to recreationists given that this will be the first good snow of the year. && .AVIATION... Updated 1115 PM MDT Wed Sep 18 2019 (19/06z TAFs) Rain will gradually come to an end over North Central Montana through 09-12z Thursday as the disturbance responsible for the activity lifts northeast into Southern Alberta. An upper level disturbance moving over the Great Basin today and on Thursday will begin to lift northeast over the Central Rockies Thursday night. Waves of scattered showers will advance north northeast across the Northern Rockies throughout the 1906/2006 TAF period ahead of this disturbance, most notably across Southwest and portions of Central Montana (i.e. KWYS, KEKS, and KHLN terminals) from late Thursday morning and into the evening hours. While VFR conditions are predominately expected throughout the next 24 hours, periods of MVFR/IFR conditions are likely beneath the heaviest precipitation. Mountain obscuration is likely across the region, especially over Southwest Montana. - Moldan && .PREV DISCUSSION... /ISSUED 316 AM MDT Thu Sep 19 2019/ Today through Friday night...primary forecast concerns throughout the period are precipitation amounts and type, especially over Southwest and Central Montana. H500 longwave trough was draped across the Western 1/3rd of the CONUS early this morning, with its axis centered from north to south over Central to Southern California. H500 height falls will occur from west to east across the Great Basin through the day today, before lifting north northeast across the Central Rockies tonight, Southeast Montana by Friday evening, and eventually the Western Dakotas by Saturday morning. The H500 vort max responsible for the overnight precipitation will continue to lift northeast over Southern Alberta through the morning hours, with subsidence overspreading North Central Montana through the afternoon hours. This will bring a gradual reduction in precipitation chances and coverage across much of North Central Montana this morning, outside of the Continental Divide where precipitation chances will linger for the day. Further to the south over Southwest Montana, precipitation chances will be on the increase from the late morning and into the afternoon hours today as "weak" (with respect to Friday through Saturday morning) divergence and ascent overspreads the area ahead of the advancing trough/closed low moving across the Great Basin. As the longwave trough pivots across the Northern Rockies tonight through Friday night, model consensus is showing that the best upper level divergence and ascent will overspread Southwest and Central Montana from the mid-morning hours on Friday through Friday evening. This timeframe will be the focus for the highest precipitation chances and amounts, along with the changeover to snow above 6500ft as cooler air associated with the trough overspreads the region and dynamic cooling also takes place. Precipitation amounts of 0.5"-1" will be possible along and southeast of a Boulder, to Kings Hill Pass, to Lewistown line from tonight through Friday night, which will make for raw conditions regardless of precipitation type given the forecasted temperatures. At this time, elevations above 8000ft in Southwest Montana could potentially see snowfall accumulations of 3-6", with up to 9" possible above 9000ft by Saturday morning. Those planning on recreating in the backcountry from tonight through Friday night should be prepared for adverse conditions including but not limited to : freezing temperatures, wet/raw conditions, and accumulating snow. - Moldan Saturday through Thursday...precipitation will gradually come to an end across Southwest and portions of North Central Montana through the afternoon hours on Saturday as the H500 longwave trough and closed low lifts into South Central Canada/Upper Mississippi Valley. Temperatures will remain well below normal in Southwest Montana on Saturday, with values closer to normal in North Central Montana. Upper level ridging will overspread the Northern Rockies Saturday night and through the day on Sunday, bringing overall quite and mild (temperatures at or above normal) conditions for the day on Sunday. Northwest flow looks to then develop over the Northern Rockies from Tuesday and into the day on Thursday, which will bring unsettled and "showery" conditions to most areas, but highs are expected to remain above normal. Beyond Thursday, model guidance this evening is in fairly good agreement that a more significant cool down could occur across the Northern Rockies as a potent upper level trough digs into the Western CONUS. - Moldan && .PRELIMINARY POINT TEMPS/POPS... GTF 62 43 63 43 / 20 20 50 60 CTB 60 38 63 41 / 40 20 10 40 HLN 61 43 60 41 / 30 40 70 80 BZN 62 40 52 38 / 30 50 90 90 WEY 60 30 44 28 / 20 60 90 80 DLN 54 39 50 36 / 60 60 80 70 HVR 68 43 69 43 / 10 10 20 50 LWT 62 41 56 41 / 10 30 80 80 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 6 AM Friday to 6 AM MDT Saturday above 8000 feet for Gallatin...Madison. && $$ http://www.weather.gov/greatfalls