


Area Forecast Discussion
Issued by NWS Missoula, MT
Issued by NWS Missoula, MT
598 FXUS65 KMSO 182102 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 302 PM MDT Sat Oct 18 2025 .DISCUSSION... KEY MESSAGES: - Strong south winds on Flathead Lake tomorrow will cause choppy conditions for boaters. - An atmospheric river will arrive in the region tonight and last through early next week causing heavy rain in the mountains. - Snow levels will fall near the end of the atmospheric river event causing several inches of snow accumulation in the mountains just after receiving around an inch of rain. - A warm break from the moisture for most of the week, and then another atmospheric river is possible around next Saturday. Strong southerly winds tomorrow will cause choppy conditions on area lakes, especially Flathead Lake tomorrow where 2 to 3 foot waves are expected in the afternoon. This lake wind event is a little unusual because of the timing, we expect winds to start increasing in the morning and remain high through the day. An atmospheric river moving into the region this evening will cause snow levels to rise with moderate to heavy rain rates expected in the mountains. The mountains of central Idaho and northwest Montana will be hardest hit, including the Bitterroot mountains in western Montana. Storm total liquid equivalent precipitation amounts will range for around 0.75 inches to over 2.0 inches in the mountains by Tuesday morning. Most of that will fall as rain. But Sunday the snow levels start to fall, and the snow to liquid ratios start to rise by late Sunday. Winter weather advisories have been issued for many mountain locations from Sunday night through Monday morning as several inches of snow are expected above 5,000 ft. With most back country roads on public lands still accessible by the public, this is cause for concern for those who might be using them. Be prepared for very wet, cold, and windy conditions. If you`re going up to higher elevations, be prepared for several inches of snow. Snow accumulations by Monday morning will be around 2-5 inches around 5,000 to 6,000 feet and upwards of 7 to 12 inches is possible above 6,000 ft. So it will start with moderate to heavy rain for a day or so, then transition to snow and accumulate a few to several inches, all while the wind is blowing 25-35 mph. These are ideal conditions for hypothermia. Through the middle of the week weather conditions will moderate with a ridge building over the region. Then, another atmospheric river is becoming more likely for next weekend. Current forecasts show that for northwest Montana, but it`s about a week out. Stay tuned! && .AVIATION...Expect increasing clouds this afternoon as an atmospheric river moves into the region. By morning, rain will have started at most area terminals with VFR to MVFR restrictions expected due to low ceilings and mist. Snow levels will be rising, so no snow impacts are expected at any terminals through Sunday. There is a low probability (less than 10 percent) for some freezing rain to briefly affect terminal KGPI tomorrow morning, though we expect the increasing cloud cover and winds to prevent the temperatures there from reaching freezing which is why the probability is so low. If, however, it does clear out for a few hours with lighter winds, it could set up a freezing rain scenario for tomorrow morning when the rain arrives. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...Winter Weather Advisory from 9 PM Sunday to 9 AM MDT Monday for Bitterroot/Sapphire Mountains...Potomac/Seeley Lake Region...West Glacier Region. Lake Wind Advisory from 6 AM to 9 PM MDT Sunday for Flathead/Mission Valleys. ID...Winter Weather Advisory from 8 PM Sunday to 8 AM PDT Monday for Southern Clearwater Mountains. && $$