102 FXUS65 KMSO 022206 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 306 PM MST FRI JAN 2 2015 ...Widespread snow tonight through Saturday morning... ...Significant system moving through the Northern Rockies Sunday through Tuesday morning bringing snow and potentially freezing rain... .DISCUSSION...Widespread light to moderate snow is expected to continue for both western Montana and north central Idaho through tonight. Temperatures are cold enough that both mountains and valleys should receive all snow, making roads slick and snow covered through Saturday morning. The best snow accumulations are expected near the Continental Divide including Glacier Park and the Seeley/Swan valleys where a dome of cold air moving into the region tonight will help to enhance snow fall. Another concern is for some blowing snow, again mainly along the Continental Divide affecting mountain passes such as Marias and MacDonald, and possibly into the northern Flathead valley. Snowfall is expected to taper off Saturday afternoon, although light snow will linger, especially in the higher terrain. A weak disturbance will be moving into the region Saturday night through Sunday which will be causing another round of widespread light to moderate snow, especially for Clearwater/Idaho counties into west central Montana during this system. Snow levels will remain low so snow will be down to all valley locations. An arctic airmass is also anticipated to move into northwest Montana, mainly impacting the Glacier park region and maybe into the Kalispell area. This arctic airmass could enhance the precipitation along the divide once again. Sunday night through Tuesday, the models are showing a very moist and warm system moving into the Northern Rockies. Snow levels will be steadily rising during this event causing snow to transition over to rain for many valley locations across north central Idaho and west central Montana. During this transition a few valley locations could receive periods of freezing rain. Even though the precipitation does change over to rain, subsurface temperatures will remain below freezing so water on area roadways could freeze. Northwest Montana should remain all snow during this event. The valleys could see any where from 6 to 10 inches of snow by Tuesday morning. The higher terrain across the whole region, including the mountain passes, are anticipated to receive 10 to 20 inches of snow. Monday night into Tuesday another arctic could nose its way into the Glacier Park region, which could enhance the precipitation once again. Wednesday into Thursday, a ridge of high pressure will be building over the Northern Rockies which will allow for the development of valley inversions. Fog development is a possibility during this period, especially after the extended period of widespread precipitation. Another disturbance appears to make its way towards the region by the end of the week, but timing and strength is uncertain at this time. && .AVIATION...Widespread light to moderate snow has spread into much of northwest/west-central Montana and north central Idaho this afternoon. Snow will continue to spread south into the rest of southwestern Montana and Lemhi County Idaho this evening. Widespread lowered ceilings and visibility will obscure the higher terrain into Saturday afternoon. KBTM, KMSO and KGPI will be the primary airfields impacted by accumulating snow, although KSMN may begin to see some snow tonight, mostly after 03/0600z. KGPI is expected to see some increased northeast winds tonight, gusting up to 30kts, mainly after 03/0600z, which could cause a period of blowing and drifting snow. Snow is expected to decrease in intensity from north to south through the day. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...WINTER STORM WATCH from Sunday afternoon through Tuesday morning ABOVE 4000 FEET for the Bitterroot/Sapphire Mountains. WINTER WEATHER ADVISORY until 11 AM MST Saturday Bitterroot/Sapphire Mountains...Butte/Blackfoot Region... Lower Clark Fork Region...Missoula/Bitterroot Valleys. WINTER STORM WATCH from Sunday afternoon through Tuesday morning Flathead/Mission Valleys...Kootenai/Cabinet Region...Lower Clark Fork Region...Potomac/Seeley Lake Region...West Glacier Region. WINTER WEATHER ADVISORY until 11 AM MST Saturday Flathead/Mission Valleys. WINTER WEATHER ADVISORY until 11 AM MST Saturday Potomac/Seeley Lake Region...West Glacier Region. WINTER WEATHER ADVISORY until 11 AM MST Saturday Kootenai/Cabinet Region. ID...WINTER WEATHER ADVISORY until 10 AM PST Saturday Northern Clearwater Mountains...Southern Clearwater Mountains. WINTER STORM WATCH from Sunday afternoon through Tuesday morning ABOVE 4000 FEET for the Northern Clearwater Mountains... Southern Clearwater Mountains. && $$