Scientific Forecaster Discussion
000 FXUS65 KMSO 180930 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 330 AM MDT Wed Oct 18 2017 .DISCUSSION... The strong winds that brought havoc over western Montana yesterday have generally subsided overnight, though some gusty winds still remain over the terrain and Continental Divide this morning. Breezy winds are forecast to continue today, peaking in the afternoon and evening hours. However, winds are not expected to be nearly as strong as yesterday. High temperatures will be slightly cooler due to less wind and a cooler air mass in place. The next feature will bring rain and high elevation snow (above 5500-6500 feet) to northwest Montana beginning this afternoon and persisting through Thursday. Strong west-southwest flow aloft will keep precipitation mainly over the terrain during this period. As the flow turns more southerly on Thursday, breezy winds combined with warm flow will allow temperatures to reach well above normal once again. By late Thursday evening, a strong cold front will begin pushing into central Idaho/northwest Montana, and continue eastward reaching the Divide by mid morning on Friday. The front itself will bring a quick burst of precipitation to most areas, followed by showery weather the remainder of Friday into early Saturday morning. Snow levels will be quite high ahead of the front but will drop to mountain pass levels behind it, thus occasional snow covered roadways above 5,000 feet could be an impact as early as sunrise Friday. Also, Friday daytime highs will be 15-20 degrees cooler compared to Thursday along with breezy westerly wind, so plan accordingly for the cool/showery conditions. A very wet and mild westerly jet stream will be focused on the Northern Rockies Saturday night through early Monday. Ample precipitation (several inches of moisture) is likely across north- central Idaho and the terrain of northwest Montana, along with windy conditions on the terrain. The Camas Prairie region of Idaho will also see windy conditions on Saturday. The valleys of western Montana will have breezy winds and will likely experience rainfall but much less compared to the higher terrain because of downsloping. Initially, snow levels may be at mountain pass levels but will quickly rise to above 6500 feet for much of the event, limiting road impacts. But those in the backcountry should prepare for frequent wet and raw conditions including the potential for accumulating snowfall above 6500 feet. && .AVIATION...Winds have decreased this morning for TAF sites, but remain gusty over mountain tops and the Continental Divide today. TAF sites are likely to see wind gusts of 20-25 kts generally after 18/2000Z, but not nearly as strong as yesterday. Precipitation will start moving into the terrain of northwest Montana by 18/2100Z and continue the next 24 hours. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None.