260
FXUS65 KMSO 161902
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
1202 PM MST Sun Nov 16 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 Wednesday: Light mountain snow with minimal impacts.

-  Next Weekend (Nov 22-23): Major pattern change likely, driven
   by an atmospheric river, bringing heavy mountain precipitation.

-  Thanksgiving Week: High confidence in a significantly colder,
   wintry pattern, with impacts including valley snowfall.


Through Wednesday:

A split-flow pattern continues through midweek, keeping the main storm
track deflected. Two weak waves of moisture will pass through:

- Today-Monday: Light showers across central Idaho and northwest
  Montana. Snow levels will remain high (near 7,000 ft), with only
  a trace to 2 inches expected on the highest passes.

- Tuesday-Wednesday: A slightly cooler system drops snow levels
  to 4,500-5,000 ft. Expect minor accumulations (generally 1 inch
  or less), with the main hazard being localized slick spots on
  passes during the overnight hours. Daytime travel should remain
  favorable.


Weekend Pattern Change (Nov 22-23):

Confidence is increasing (60-70% probability) in a major shift as
an atmospheric river (AR) targets the Pacific Northwest. This
system will be supported by a strong (130+ kt) upper-level jet,
creating conditions favorable for widespread rising motion and
heavy precipitation.

- Heavy Mountain Precipitation: There is a high potential for
  heavy precipitation in the mountains.
   *The NBM 4.3 90th percentile (which often verifies in ARs)
    shows ~1.00 inch of liquid precipitation (QPF) in 24 hours
    (ending 5 PM Saturday).
   *ECMWF Ensemble 90th percentile shows 1-2 inches of liquid
    equivalent for the mountains along the Idaho/Montana border.

- Snow Levels (Primary Forecast Challenge):
   *Milder Scenario: A more northward AR track would keep snow
    levels high, limiting major impacts to areas above the valley
    floors.
   *Colder Scenario: A slightly southward track supported by some
    ensemble members would drop snow levels significantly. The
    NBM 4.3 10th percentile shows snow levels near 2,900 ft on
    Saturday across northwest Montana, raising the slight
    possibility of accumulating wet snow on valley floors.


Thanksgiving Week:

This period carries the highest potential for widespread, high-
impact weather. While specific details remain uncertain, guidance
favors a deep, cold upper-level trough developing along the West
Coast rather than a quick frontal passage.

- Temperatures: Confidence is high in a shift to substantially
  colder conditions.
   *The NBM 4.3 shows a 50-60% chance of valley high temperatures
    staying below freezing on Tuesday, rising to 70-80% by
    Wednesday.
   *The moderate probability (30-60%) of lows in the mid-teens and
    lower expanding across all western Montana valleys by
    Wednesday morning.
   *Subzero lows are possible later in the week, especially along
    the Continental Divide.

- Snow: The large-scale (synoptic) setup strongly favors low-
  elevation snow.
   *Ensemble guidance suggests a potential surface low tracking
    from southern Idaho toward southwest Montana, which is a
    favorable pattern for significant valley snow, particularly
    north and west of the low path.
   *Scenario Uncertainty: If the trough digs farther west, the
    region could stay somewhat milder with less precipitation.
    However, a deeper trough could also draw Arctic air south
    sooner, potentially as early as Monday-Tuesday.
   *Persistent Wintry Threat: Once the cold air settles, an
    active northwest flow and an unstable atmosphere may support
    ongoing snow showers or heavier squalls. This could lead to
    persistently slick road conditions and sudden reductions in
    visibility on passes and valley roads.



&&

.AVIATION...An upper low lifting through the Great Basin will
transport moisture and weak lift across the Northern Rockies
through Monday. The first round of light showers will spread south
to north this afternoon, followed by additional showers tonight
into Monday. The most persistent showers and periodic reductions
to MVFR/IFR ceilings and visibility are expected across north-
central Idaho and northwest Montana, particularly tonight and
Monday morning.

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

&&

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

$$