959
FXUS65 KMSO 040846
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
146 AM MST Thu Dec 4 2025

.DISCUSSION...

KEY MESSAGES:

-  A prolonged period of winter weather starts on Thursday lasting
   through the weekend

-  Heavy mountain snow, along with a wintry mix in the valleys
   will make for difficult travel conditions

-  Unsettled winter weather will continue into next week

Interesting and active weather period begins around sunrise today!
While there is moderate or better confidence snow will be
measured in feet in the mountains, there remains some uncertainty
for valleys and how long the atmosphere will support initially
snow, then a transition to rain that may include in some locations
a brief period of freezing rain. Satellite currently has a fetch
of Pacific moisture rotating around high pressure off the west
coast, putting the northern Rockies in northwest flow.

Snow will begin between 4 and 8 am, mainly in the mountains north
and south of MT-200 and I-90 west of Missoula. By afternoon,
valleys along US-93 will begin to receive flurries to light snow.
Snow intensity will likely preclude any accumulation through
sunset on roads but a light dusting over sidewalks could create
slippery walking conditions. After sunset through Friday morning a
trace to 2 inches throughout western Montana is possible. This is
not the part of the system that will be measured in feet and 3-6
inches by Friday afternoon is forecast at Lookout, Lolo, and Lost
Trail Passes.

Friday afternoon flow aloft flattens more westerly, this will
mark the changing of valley temperatures I-90 and south. Snow is
expected to mix with rain and for some valleys precipitation may
briefly cutoff as weak downsloping initiates. At this time a deep
and long lived fetch of Pacific moisture will begin to interact
with our mountains. While precipitation is not forecast to
completely end, it will lighten up Saturday afternoon. At that
time most mountain ranges will have received 1 to 2 inches of
liquid equivalent, that will fall as 1 to 2 feet of snow.

Looking closer at valleys from Friday evening onward, as said I-90
southward will mix with rain or precipitation stops. Temperatures
however will remain right around freezing. It is possible that
overnight temperatures cool a degree or two allowing for a brief
period of freezing rain Saturday morning. The area of highest
concern would be the I-90 corridor, exercise caution if driving
over bridges between Missoula and St Regis Saturday morning. Snow
levels by Saturday evening will be rising over 4000 feet.

Precipitation continues most of the weekend with light snow in the
mountains and light rain, drizzle, or overcast conditions in the
valleys.

Monday afternoon, another deep and long lived fetch of moisture
pushes onshore the Pacific northwest. This fetch of moisture will
be riding a 140 to 160 mph Jet Stream. Expect very breezy days,
severe valley downsloping causing temperatures to spike into the
40s, and plentiful mountain moisture. There are differences in the
models on placement of the jet stream. One model has the jet well
north in Canada and snow levels around 7000 feet, another has it
directly over west-central Montana and snow levels 4000-5000 feet.
Better details are expected in future forecasts as this system
comes into focus.



&&

.AVIATION...Valley stratus is expected to begin the day, while mountains
will remain obscured. An incoming system today will continue
widespread mountain obscuration and a return to MVFR/IFR
visibility with snow developing during the morning. Light snow
develops at KGPI and KMSO as early as 1200z.


&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Watch from late Thursday night through Saturday
     afternoon for Bitterroot/Sapphire Mountains...Lower Clark
     Fork Region...Potomac/Seeley Lake Region...West Glacier
     Region.

ID...Winter Storm Watch from late Thursday night through Saturday
     afternoon for Northern Clearwater Mountains...Southern
     Clearwater Mountains.

&&

$$