Winter Weather Advisory 58, NWS Missoula, MT

Area Forecast Discussion
National Weather Service Missoula MT
306 AM MST Sun Dec 5 2021

.DISCUSSION...Widespread shower activity continues to develop
this morning under moist westerly flow. A surface cold front
continues to slowly move southward, having just crossed into
Silver Bow, Deer Lodge, and Lemhi Counties as of 300am. Shower
activity will continue through the late morning hours before drier
air moves in from the northwest. Winter Weather Advisories have
been extended through 800am across the Bitterroot/Sapphire
Mountains, the Potomac/Seeley Lake and Butte/Blackfoot regions,
where additional accumulations of 1 to 3 inches are possible. Be
prepared for slick conditions if you plan to travel across these
aforementioned areas as temperatures will continue to drop below
freezing the next few hours.

Snowfall returns across the Northern Rockies Monday morning as a
shortwave trough embedded within northwesterly flow moves across
the area. Snowfall amounts across northwest and southwest Montana
have trended lower, with generally less than one inch expected
across valley locations. The main reason for this change is the
lack of a surface low now present across central Idaho as
advertised by model guidance a few days ago. Nonetheless, medium
to high confidence still exists for accumulating snow along the
I-90 corridor in west-central Montana and across Clearwater and
Idaho counties, areas typically favored under moist northwesterly
flow. Impacts are still expected for the Monday morning commute.
Temperatures will moderate near freezing by the afternoon hours
for valley locations, helping to mitigate travel impacts.
Scattered snow shower activity will continue into Tuesday, with
minor accumulations, generally less than half an inch, expected.

The Northern Rockies will remain under a progressive
northwesterly flow pattern through Friday. This pattern will
support periodic snowfall, particularly for mountain ranges along
the ID/MT border and in northwest Montana. The next pacific storm
system arrives Wednesday morning as a shortwave trough moves
across British Columbia into northwest Montana. Widespread
snowfall will develop across northwest Montana Wednesday morning
as pacific moisture is lifted by a warm frontal boundary. Moderate
confidence exists for accumulating snowfall to impact the
Wednesday morning commute across the Kootenai/Cabinet region, the
Flathead Valley, and in the West Glacier region. A cold front will
track across the area Wednesday night into Thursday. Scattered
snow showers will develop across the area Thursday, with the bulk
of accumulating snow expected across the Clearwater, Bitterroot,
Mission, and Swan Mountains.

Model guidance continues to remain in good agreement with a
colder air mass settling in across the Northern Rockies Thursday
into Friday. Much of the area will experience low temperatures in
the teens to potentially below zero for areas along the
Continental Divide Friday and Saturday morning. /Lukinbeal

&&

.AVIATION...Scattered rain and snow shower activity will
continue along and south of the I-90 corridor through 05/1800z.
Drier air begins to push into the Northern Rockies after 05/1800z,
leading to a decreasing trend in cloud cover. A cold front will
continue to march south across southwest Montana through 05/1200z.
Scattered snow showers will lead to temporary visibility
reductions at KBTM through 05/1500z. Northwesterly winds will
prevail across the airspace today, with gusts around 20 knots
expected. /Lukinbeal

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory until 8 AM MST this morning
     Butte/Blackfoot Region.

     Winter Weather Advisory until 8 AM MST this morning
     Bitterroot/Sapphire Mountains.

     Winter Weather Advisory until 8 AM MST this morning
     Potomac/Seeley Lake Region.

ID...Winter Weather Advisory until 7 AM PST this morning Southern
     Clearwater Mountains.

&&

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