Bigfork, Montana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

658
FXUS65 KMSO 220557 AAC
AFDMSO

Area Forecast Discussion...UPDATED
National Weather Service Missoula MT
1057 PM MST Sun Dec 21 2025

.DISCUSSION...

KEY MESSAGES:

-  Forecast Shift to Colder/Snowier Tonight: Weather models are
   struggling to resolve the trapped cold airmass. Expect more
   snow and wintry mix rather than rain for many areas tonight.
   Winter weather advisories have expanded. Watch out for black
   ice.

-  Unsettled Holiday Week: Periodic disturbances continue through
   the week. A cold front Friday will drop snow levels to valley
   floors.

-  New Year`s Eve Outlook: A potential atmospheric river could
   bring milder, wetter, and windier conditions to end the year.

This Afternoon through Monday Night: The primary forecast
challenge has been the stubborn cold and dry airmass currently
entrenched across the region. While anomalously high moisture is
streaming in from the westkeeping the atmosphere saturated and
limiting solar insolationmany high-resolution models are
struggling to resolve the cold pool, eroding it far too quickly.
In contrast, the GFS model is handling the low-level thermal
profiles much better, maintaining the colder air in place.
Consequently, we have leaned the forecast heavily toward this
colder solution. With this adjustment, the precipitation type for
tonight`s event is expected to remain predominantly snow or a
wintry mix, rather than a quick transition to rain. We have
updated and expanded Winter Weather Advisories to account for this
prolonged period of snow, mixed precipitation, and the
development of black ice.

Valley Precip Type: The more open lower valleys, extending from
the Flathead to the Bitterroot and Camas Prairie, Idaho, are
still susceptible to a mixture of rain and snow due to slightly
better mixing, but the window for pure rain has narrowed.

Road Hazards: With the recent stretch of cold temperatures,
pavement temperatures remain low. Above 4000 feet, black ice
formation is a significant concern, particularly on bridges and
overpasses. For elevations below 4000 feet, slick travel will
likely be driven by slush accumulation on roadways.

Tuesday through Thursday (Christmas Day): The pattern remains
active. By Tuesday, our southern zones will see the remnants of
the California atmospheric river. This looks to be a narrow
corridor of moisture that could bring light snow to mountain
passes and perhaps a light wintry mix to the valleys Tuesday
night.

For the holiday proper (Christmas Eve into Christmas Day), a deep
trough over the eastern Pacific will eject several shortwaves
into the Pacific Northwest. One such wave is projected to develop
a surface low over Washington on Wednesday. This setup could
induce enough easterly flow to push a wedge of Arctic air westward
through Marias Pass and into Essex. Elsewhere, additional
precipitation is likely, with night-time occurrences potentially
falling as a wintry mix.

Friday through Next Weekend: A more robust wave is forecast to
arrive Friday, driving a sizeable cold front through the Northern
Rockies. This will likely cause snow levels to crash to valley
floors, transitioning precipitation to snow showers.

Looking ahead to next weekend, conditions actually look quite
decent relative to the active week. Expect cooler temperatures and
persistent mountain snow showers, but perhaps a break from the
heavier organized precipitation.

Extended Outlook (New Year`s Eve): Ensembles are hinting at a
pattern shift to close out 2025. Current guidance depicts an
atmospheric river initially targeted at British Columbia shifting
southward over the Pacific Northwest and Northern Rockies around
New Year`s Eve. If this solution verifies, we would expect a
transition to much milder temperatures, significantly higher snow
levels, and increased wind and precipitation.


&&

.AVIATION... The main concern is the persistence of low ceilings
and mixed precipitation types. With the forecast trending colder,
terminals such as KGPI, KHRF and KMSO are more likely to see
prolonged periods of snow or wintry mix rather than a clean switch
to rain overnight. Expect IFR/LIFR conditions to dominate as the
low levels remain saturated. Mountain obscuration will be
widespread. LLWS may be present at times as strong westerly flow
aloft overrides the trapped valley cold pools after 0500MST(1200Z)
Monday Dec. 22 across southwest Montana, along the Divide and
Lemhi County.



&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory until 11 AM MST Monday for
     Butte/Blackfoot Region...Flathead/Mission Valleys...
     Kootenai/Cabinet Region...Lower Clark Fork Region...
     Missoula/Bitterroot Valleys...Potomac/Seeley Lake Region...
     West Glacier Region.

     Winter Weather Advisory until 9 AM MST Monday for
     Bitterroot/Sapphire Mountains.

ID...Winter Weather Advisory until 10 AM PST Monday for Northern
     Clearwater Mountains...Southern Clearwater Mountains.

     Winter Weather Advisory until 9 AM MST Monday for Eastern Lemhi
     County...Western Lemhi County.

&&

$$