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000
FXUS65 KMSO 030939
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
239 AM MST Sun Dec 3 2023

.DISCUSSION...
A series of pacific storm systems will impact the Northern
Rockies through the upcoming week. The next Pacific trough, as
seen in GOES-18 Water Vapor imagery, is beginning to move onshore
in the Pacific Northwest and British Columbia early this morning.
A warm front, associated with this trough, will spread
precipitation across Idaho and Clearwater Counties by the late
morning hours. Precipitation will spread along the ID/MT border
during the early afternoon, before tracking across the rest of
western Montana by the mid-afternoon. Winter weather advisories
remain in effect for Clearwater Mountains, the Bitterroot and
Sapphire Mountains, and the Lower Clark Fork Region, where higher
confidence exists for moderate snow and travel impacts, primarily
for mountain pass areas. Snow levels will start this morning at
2,000 feet, but will quickly climb above 4,000 feet in Idaho by
late this morning. Snow levels in Montana will climb above 4,000
feet by the early to mid-afternoon as a southerly pressure
gradient brings mild air northward.

Black ice is a concern Sunday night into Monday morning. As
precipitation changes over rain, cold ground temperatures may
lead to icy conditions for untreated surfaces Sunday night.
Northwest Montana valleys and areas along Montana Highway 83 and
200 will be the most susceptible for black ice formation.

A transitory ridge of high pressure will amplify across the
Northern Rockies late Monday into Tuesday. Southwesterly flow will
bring a mild Pacific air mass across the region, with
temperatures approaching record values (upper-40s to 50s) and snow
levels climbing above 8,000 feet! Model guidance continues to
show an atmospheric river along the western periphery of the
ridge. This plume of moisture will extend across northwest OR
into northeast WA and across north-central ID and northwest
MT. Precipitation through Tuesday night will primarily focus
across the Cabinet and Purcell Mountains.

A broad Pacific trough will move across the Northern Rockies late
Wednesday into Friday. Snow levels will fall down into the
2000-3000 feet range by Thursday night as a cold front tracks
across the region. The trajectory of this system will favor
mountain snow along the ID/MT border and in northwest Montana.
Snow showers will continue into Friday under northwesterly flow.
/Lukinbeal


&&

.AVIATION...The next pacific storm system arrives late this
morning into the afternoon across the Northern Rockies airspace.
Precipitation, associated with a warm front, will track west to
east across Idaho and Clearwater Counties between 03/1600-1800Z,
reaching western Montana after 03/1900Z. Snow will initially fall
down to 2,000 feet, before snow levels quickly rise above 4,000
feet south of I-90 by 03/2100Z. Snow levels across northwest
Montana will rise above 4,000 feet after 04/0000Z as the warm
front continues northward. Southwest-west winds will increase
after 04/0000Z along the Continental Divide and over the higher
terrain. /Lukinbeal

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory from 11 AM this morning to 5 AM MST
     Monday for Bitterroot/Sapphire Mountains...Lower Clark Fork
     Region.

ID...Winter Weather Advisory from 10 AM this morning to 4 AM PST
     Monday for Northern Clearwater Mountains...Southern
     Clearwater Mountains.

&&

$$