512
FXUS65 KMSO 052013
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
113 PM MST Fri Dec 5 2025

.DISCUSSION...

KEY MESSAGES:

-  A prolonged period of winter weather lasting through at least
   the weekend

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

-  Gusty westerly winds from Tonight into Saturday

-  Unsettled winter weather will continue into next week with
   potential for significant rainfall below 5000 ft midweek

The next push of precipitation is beginning to move into north
central and northwest Montana this afternoon. This feature will
cause light to moderate snow for the majority of the region with
the expectations being mainly rain for the lower valleys of north
central Idaho, northwest Montana, Mission valley and Bitterroot
valley. After the passage of this disturbance anticipated gusty
westerly winds developing overnight causing downsloping effects
especially in the broader valleys. The HiRes models continue to
depict the development of snow bands developing during the evening
hours. These bands will be capable of producing heavy snowfall (1
to 2 inch per hour rates) along with gusty winds with the
greatest area of concerning being Seeley/Swan Valley south
through the Sapphire range into southwest Montana. Multiple winter
storm warnings and advisories are still in effect from the
potential impacts from this next wave.

Snow is expected to linger in the higher terrain, especially along
the Montana/Idaho border on Saturday through Saturday. While the
valleys experience off and on rain/snow showers but also gusty
westerly winds throughout the period. Snowfall totals for the next
48 hours ending Sunday morning show the mountains along the
Montana/Idaho border, Mission range and Bob Marshall wilderness
should receive 1 to 2 feet of new snow. While the mountains of
extreme northwest Montana, including Glacier and southwest Montana
are expected to receive 6 to 12 inches of snow. Once again the
valleys will be receiving a rain/snow mix during this timeframe
along with downsloping effects so 48 hr moisture amounts appear
to range from 0.20" to 0.60" with snow accumulations being in the
1 to 4 inch range.

Another weak pulse of moisture appears to push through the
Northern Rockies Sunday night causing an increase in the shower
activity.

The models continue to come in better alignment with a significant
atmospheric river (AR) impacting the Northern Rockies late Monday
through at least Wednesday. Snow levels will be rising to around
5000 feet in the north and 7000 feet in the southern part of the
forecast area by Tuesday morning. Snow levels do appear to lower
by a 1000 feet by Wednesday morning but then rise back up by
Thursday. This AR event has the potential to bring near historic
moisture amounts to the region for this time of year, especially
along the Montana/Idaho border. The rainfall totals during this
event appear to be between 1 to 3 inches with the heaviest amounts
being over Idaho/Clearwater counties into northwest Montana. The
valleys of Lemhi county and southwest Montana are expected to
receive between 0.25" to 1.5" of rain. The areas above the snow
level should anticipate 1 to 2 feet of additional snow. The
biggest concern is the potential for ponding of water, significant
increase in stream flows and rock/mud slides.

This active weather pattern appears to continue for the latter
part of the work week into next week as snow levels are
anticipated to lower.



&&

.AVIATION...Expect little to no improvement in flying weather
conditions through the rest of the day at all regional terminal
locations as the valley inversions, freezing fog, and low stratus
hold firm and snow begins to fall. A surge of Pacific moisture
is moving into the Northern Rockies increasing mtn obscurations
and revamping precipitation intensities. Snow/freezing levels will
remain the trickiest part of the forecast heading into the
weekend. Snow will fall to most valley floors before slight
warming increases the snow/freezing levels into Saturday. Defined
snow bands and or squalls will accompany the surge of pacific
moisture bringing localized major deteriorations to flying weather
and periodic lowering of freezing/snow levels to valley floors.
Gusty westerly winds increase into Saturday morning helping mix
out some of the lowest stagnant layers but introducing some
mehcanical turbulence and low-level wind shear.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Warning until 5 PM MST Saturday for
     Bitterroot/Sapphire Mountains...Lower Clark Fork Region...
     Potomac/Seeley Lake Region.

     Winter Weather Advisory from 5 PM this afternoon to 5 PM MST
     Saturday for West Glacier Region.

     Winter Weather Advisory until 11 PM MST this evening for
     Butte/Blackfoot Region...Missoula/Bitterroot Valleys.

ID...Winter Storm Warning until 4 PM PST Saturday for Northern
     Clearwater Mountains...Southern Clearwater Mountains.

&&

$$