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FXUS65 KMSO 082143 AFDMSO

Area Forecast Discussion National Weather Service Missoula MT 243 PM MST Fri Dec 8 2023

DISCUSSION
A short wave sliding through northwest Montana will continue to bring snow showers today, mainly focused from Bigfork south along the Mission Range including Seeley/Swan Valley.

Those showers will be diminishing this evening with clearing in most areas due to a transient ridge of high pressure. Weak cold pools will have the ability to build in area valleys leading to patchy fog and or low stratus. These cold pools will also help to negate early effects of downsloping for the next system Saturday evening.

A plume of significant moisture will be moving into the Northern Rockies Saturday night through Sunday. This moisture will bring a decent amount to snow to the higher terrain, especially along the Montana/Idaho border. Lookout Pass has over an 80% chance of receiving more than 8 inches of snow Saturday night through Sunday night with the heaviest snowfall rates occurring late Saturday night. While the valleys will start off as snow Saturday night with widespread 1 to 3 inches by Sunday morning. Snow levels will be rising during the overnight into Sunday. The valleys south of the I-90 corridor appear to transition to a wintry mix by Sunday morning. Depending on how strong valley inversions are, the potential exists that a few valleys of north central Idaho and west central Montana could receive a period of freezing rain by Sunday morning.

Another feature that is being monitored is gusty southerly winds developing Saturday afternoon and lasting until Sunday for Lemhi & Idaho counties into southwest Montana. These southerly winds will cause some downsloping effects and enhanced warming mitigating the snow impacts for areas such as the Camas Prairie of Idaho, Bitterroot valley and the valleys around the Anaconda/Pintlar ranges.

Another weak disturbance will pass through the region on Monday keeping showers lingering across the Northern Rockies. This disturbance has the potential of keeping snow impacts lasting until Tuesday morning, especially over mountain passes.

The models continue to indicate that a fairly strong ridge of high pressure will be developing over the Northern Rockies which will cause valley inversions with low stratus and fog developing by mid next week.

AVIATION
Gusty west winds have subsided for most valley locations, that said mid-level winds remain 20 to 25 kts. A few showers remain along the Mission Mountains and areas east. KGPI may have showers in the vicinity through 09/00z while remaining shower activity in the mountains will diminish after 09/03z.
Transient high pressure builds in the Northern Rockies overnight and patchy fog will be possible at area terminals. Another system will begin to affect the region Saturday evening.



MSO WATCHES/WARNINGS/ADVISORIES
MT...Winter Weather Advisory from 5 PM Saturday to 5 AM MST Monday for Bitterroot/Sapphire Mountains...Lower Clark Fork Region.

Winter Weather Advisory until 9 PM MST this evening for Flathead/Mission Valleys
Potomac/Seeley Lake Region
West Glacier Region.

ID...Winter Weather Advisory from 4 PM Saturday to 4 AM PST Monday for Northern Clearwater Mountains...Southern Clearwater Mountains.

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