106
FXUS65 KMSO 171111
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
411 AM MST Mon Nov 17 2025

.DISCUSSION...

After a persistently mild November, all indications point to a
major and abrupt pattern change arriving for Thanksgiving week.
This will likely be the first widespread, low-elevation winter
impact of the season.

Residents should use the relative calm of the coming week to
finalize winter preparations, especially ahead of holiday travel.

KEY MESSAGES:

- Through Friday: Continued mild, with two weak waves bringing
  light showers. The main hazard shifts to patchy, locally dense
  fog during the overnight/morning hours.

- Next Weekend (Nov 22-23): A potent atmospheric river will bring
  heavy mountain precipitation (1-2 inches liquid) and rain to
  the valleys. Snow levels of 4000-5000 ft will mean significant
  snow at mountain passes.

- Thanksgiving Week: High confidence in a significantly colder,
  wintry pattern. The coldest air of the season will arrive, with
  high probabilities for sub-freezing highs and valley snowfall.

Through Friday:

The mild, split-flow pattern continues. Temperatures will remain
10+ degrees above average, with valley highs in the 50s possible
through Tuesday. Two weak waves will bring periods of showers.

- Today (Monday): Slow-moving waves will continue light showers,
  mainly in northwest Montana. Tonight, the main concern is
  patchy fog development. Latest guidance shows breaks in the
  clouds from north-central Idaho into west-central Montana, which
  could be just enough to trigger it.

- Tuesday-Wednesday: A shortwave tracking into southern Alberta
  on Tuesday will bring more showers (focused on northwest
  Montana) and light westerly breezes elsewhere. Upper ridging
  builds in Wednesday, allowing for a little bit more sunshine.

- Thursday-Friday: The ridge will bring a return of fog and/or
  low clouds by Thursday and Friday mornings. Model soundings
  depict the potential for locally dense fog in the valleys.

This Weekend (Nov 22-23):

There has been a slight change to the evolution of the atmospheric
river pattern for the weekend..models have shifted the upper jet
further north initially, but the main plume continues to be aimed
at the Northern Rockies.

- Heavy Mountain Precipitation: The latest NBM shows a 48-hour
  total liquid precipitation of 1 to 2 inches in the mountains,
  specifically along the Idaho/Montana border and in the Mission,
  Swan, and Lewis ranges.

- Snow Levels (The Primary Impact): Snow levels are forecast to
  be 4000 to 5000 feet on Saturday, lowering on Sunday. This
  resolves much of yesterday`s uncertainty. This means the primary
  impact will be rain in the valleys but snowfall for mountain
  passes. Snow levels fall to around 3300 feet by Monday morning
  across northwest Montana which could support some valley snow
  there.

Thanksgiving Week:

This period carries the highest potential for widespread, high-
impact weather. Confidence remains high that the coldest trough
and cold front of the season will arrive Monday into Tuesday,
bringing gusty winds and possible valley snowfall.

-Temperatures: Probabilities continue to increase for a transition
 to prolonged cold. The NBM shows a 60% to 70% probability for
 high temperatures at or below freezing by Wednesday in western
 Montana valleys. Highs on Wednesday and Thanksgiving could
 struggle to get out of the low 30s. The lower valleys of north-
 central Idaho will also struggle to get out of the 30s.

-Climatological Context: To put this in perspective, the last
 time this region saw this cold of a pattern for Thanksgiving was
 November 28, 2019. On that day, Missoula and Kalispell saw a high
 of 26F, Orofino was 35F, and Butte was 14F.

-Snow: While exact details on "how cold it will get" and "how
 much snow" remain uncertain, the synoptic setup is becoming
 clearer. Ensemble means depict a sizeable Arctic air mass pushing
 south out of Canada, with the core of the coldest air likely
 staying east of the Divide(for now). This pattern would allow
 continued Pacific disturbances to provide periods of overrunning
 snow. This creates a persistent threat for slick roads and
 impacts to holiday travel.


&&

.AVIATION...Shortwaves will continue to bring light showers across
the region, especially across northwest Montana today and Tuesday.
Periodic reductions to MVFR/IFR ceilings and visibility are
possible this morning.

Elsewhere, VFR conditions will largely prevail. Mountain
obscurations will be possible at times. Surface winds will remain
relatively light across the region. Patchy valley fog is also a
concern this morning and also Tuesday morning where partial
clearing occurs.


&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&

$$