109 FXUS65 KMSO 060955 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 355 AM MDT Wed Oct 6 2021 ...Fall weather returns with snow possible by early next week... .DISCUSSION...Today is the transition day as a relatively dry cold front will move across the region. The front has made it into north-central Idaho early this morning without too much fanfare. Expect clouds and showers there today with highs only in the 50s to lower 60s. Wildfire smoke from California was seen as haze hanging around the mountains and smoke observed in a few valley locations yesterday. Today’s west winds that develop will alleviate the smoke. Expect westerly winds between 10 and 20 mph with a slight chop on area lakes this afternoon. Across southwest Montana and Lemhi County today: The first of two waves is currently moving north across southwest Montana early this morning. It is producing rain showers and a fair amount of stiff southerly winds ahead of it. This wave will exit later this morning giving way to temperatures warming back into the 60s and 70s. A second wave will move in a similar path this afternoon and besides gusty winds showers, a few isolated thunderstorms are possible. Looking at the bigger picture, much of the energy from the Pacific trough, responsible for today's front, gets shunted north into Canada tonight and we stay under southwest flow through Friday. Above normal atmospheric moisture levels combined with embedded weak waves will bring showers mainly to the south of Missoula both Thursday and Friday. Forecast model soundings show meager instability, so there is a low probability of isolated thunderstorms from Salmon to Butte. Expect seasonable temperatures, breezy and dry afternoons both Thursday and Friday across northwest Montana. With the cooler airmass in place, frosty mornings between Thursday and Saturday are expected. A transient upper level ridge will build by Saturday but will shift to central and eastern Montana by Sunday ahead of the next trough. Saturday should turn out to be a nice fall day with highs warming into the 50s to lower 60s for many valley locations. Also expect breezy winds to develop on Saturday and get a little stronger by Sunday with gusts potentially as high as 20 to 30 mph across western Montana. Rain is expected to arrive from north- central Idaho into northwest Montana by Sunday afternoon. It could feel quite chilly and damp for places like Pierce, Thompson Falls, Libby, Troy and Yaak when the rain cools the air down to 50 degrees or even the upper 40s. There has been a slight faster trend in the precipitation, which could equate to showers developing earlier than expected in places like Kalispell, Glacier National Park and/or Missoula. All attention will be drawn to the next incoming trough on Monday and Tuesday. This trough could contain the coldest air of the season, especially that it will have originated over the Bering Sea, west of Alaska. Temperatures at approximately 9,000 feet could be as cold as 14 degrees Fahrenheit as the trough moves over us on Monday. Ensemble weather models indicate that the strong upper level jet will carve a deep trough across the western U.S., causing it to possibly cut off over the Four Corners region or points north, leaving us with a weaker trough passage. The threat for snow continues to be a concern though. The probability for greater than an inch of snow is pretty high for the mountains and also southwest Montana valleys. The probability for greater than 2 inches, 48 hours ending daybreak Wednesday is between 70 and 80 percent for Georgetown Lake, Butte, Anaconda, McDonald Pass, Gilmore Summit and Lost Trail Pass. As mentioned in the previous discussion, snow levels could be the lowest this fall, near 4,000 feet. Some valley locations could even experience their first snow flakes of the season. It will be a shock for many people when high temperatures struggle to get out of the 30s or 40s on Monday and Tuesday! Low temperatures in many of the valleys could dip down to the lower 20s which would not only kill much of sensitive vegetation holding on for dear life, but could be a concern for irrigation. Stay tuned. && .AVIATION...Gusty south winds at BTM should end by 06/1200Z as a wave with showers moves off to the northeast. A relatively dry cold front will move across the region today and will bring westerly winds, gusting to 20 knots at MSO and GPI. The front will be slow to get to BTM and SMN as showers with gusty winds and possibly an isolated thunderstorm could impact those terminals between 06/2100Z and 07/0100Z. On Thursday more showers are possible at both SMN and BTM later in the day. && .CLIMATE...Missoula and Kalispell both set a daily record high temperature yesterday. The high of 84 in Missoula broke the old record of 81 set in 1979 while Kalispell warmed to 80 degrees which broke the old record of 77 set in 1958. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. && $$