591
FXUS65 KMSO 111104
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
404 AM MST Thu Dec 11 2025

.DISCUSSION...

KEY MESSAGES:

- Heavy rain and flooding threats shift further north towards NW
  Montana.

- Record warm overnight lows will aid in snow melt through Friday
  morning.

- Snow returns to northwest Montana, and especially the Seeley-
  Swan Valley tonight.

Strong mid level winds along with stable mountain layer has
allowed for the development of mountain waves to form over the
Northern Rockies. Localized areas throughout the region, but
particularly in the broader valleys have experienced wind gusts up
to 50 mph throughout the night. These winds have caused trees and
power lines to fall due to the wet soil. The winds are expected to
diminish throughout the day.

The plume of moisture associated with the atmospheric river has
shift to the north along the Canadian border. The excessive
rainfall along with snow melt has created flooding of small
streams across Lincoln county. The Yaak river near Troy is now
forecasted to hit minor flood stage later today.

The moisture is anticipated to shift southward and be more over
north central Idaho and west central Montana by this afternoon.
This shift could cause more areas to be affected by flooding
later, so a flood watch continue for the areas that have the best
chance of being affected.

Tonight some arctic air is expected to push over the Continental
Divide around Glacier National Park. This colder air will cause
snow levels to drop dramatically allowing for the potential of a
couple of inches of new snow and maybe even pockets of freezing
rain.

The atmospheric river moves northward and out of the region by
Friday as a ridge of high pressure builds along the Pacific coast.
The ridge slides over the region by this weekend causing a drying
trend, but valley inversions along with fog and low stratus could
become an issue. The Northern Rockies appear to move back in to an
active weather pattern by Tuesday of next week.


&&

.AVIATION...The atmospheric river continues across northwest
Montana this morning causing low ceilings and reduced visibility
especially to KGPI. The moisture stream shifts slightly to the
south throughout the day aligning more over north central Idaho
and west central Montana having more of an impact over KMSO by the
afternoon. Another concern today, especially during the morning
hours, is the strong mid level winds along with a mountain top
stable layer. These conditions are creating mountain waves over
the Northern Rockies producing localized strong westerly winds
along with significant wind shear. The winds are expected to
decrease throughout the morning.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Flood Watch through this afternoon for Flathead/Mission
     Valleys...Kootenai/Cabinet Region...Lower Clark Fork
     Region...Potomac/Seeley Lake Region...West Glacier Region.

     Wind Advisory until 8 AM MST this morning for Flathead/Mission
     Valleys...Kootenai/Cabinet Region...Potomac/Seeley Lake
     Region...West Glacier Region.

ID...Flood Watch through this afternoon for Northern Clearwater
     Mountains...Orofino/Grangeville Region.

&&

$$