744
FXUS65 KMSO 292029
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
129 PM MST Sat Nov 29 2025

.DISCUSSION...

KEY MESSAGES:

- Weak system will bring light snow or flurries (under an inch)
  near the Montana/Idaho border later today into tonight.

- Widespread winter travel impacts Monday through Tuesday as an
  overrunning snow event occurs.

- Active pattern continues through late week: Possible
  subtropical plume combined with colder ground temperatures could
  bring more slick travel.


Today: The Arctic air mass in place across western Montana may
moderate slightly today. There is a shortwave that will dive
southeastwards from BC, and cut-off briefly over southern Idaho.
Meanwhile thanks to the mild waters (46 degrees F) of Flathead
Lake, the moisture has risen and become low clouds over the Polson
and Mission Valley. Flurries are possible there.

As the weak surface reflection of the trough moves into
southeastern Idaho Sunday morning, this will enhance the
northeasterly wind gradient overnight, mainly felt in the higher
elevations (10-20 mph). This system may be able to moisten the
mid-levels just enough that there could be flurries or light snow
near the Montana/Idaho border tonight. Accumulations will be
light, generally less than one inch. There may be residual clouds
near Flathead Lake on Sunday.

Upcoming widespread winter system Monday-Tuesday:
Slick travel impacts to mountains and valleys are expected from
Monday to Tuesday due to an overrunning snow event enabled by the
existing cold air mass in place. A trough will dive southeastwards
out of British Columbia and bring with it, 160% of normal
atmospheric moisture. This northwest flow pattern favors a snow-
making pattern for us because the moisture is mostly conserved
aloft, meaning any Pacific moisture that it brings with it will
not have dried up due to upstream mountain ranges. A key forecast
problem will be when the snow will develop. Forecast soundings
depict moistening up during the day Monday from north to south.
Snow may fall during the day initially, which may have a hard time
sticking to road surfaces thanks to incoming solar influences. If
it arrives sooner, like in the morning, then sub-freezing
surfaces may become slick(across northwest Montana). Highs on
Monday will range from the upper 20s in the north to the 30s and
40s over Idaho. By nightfall, any untreated surfaces could become
quite slick underneath with fresh snow falling on top.

This pattern favors more of the accumulating snow across the
upslope mountains and valleys along the Montana/Idaho border, and
remainder of the mountains in northwest Montana. Thanks to the
cold air in place, the interior valleys may be able to receive
several inches of snowfall out of this. Valley snowfall ranges 2
to 5 inches(locally higher), while mountains(excluding across
southwest Montana), range 4 to 8 inches. Some of the upper
percentiles have over 0.40 of water forecast for
upslope/foothills areas along the Swan Range, and depending on the
snow-to-liquid ratios, this could end up being 5 to 8 inches!).
The probabilities are around 30% for greater than 8 inches from
the Mission Mountains to the Glacier Region mountains. Weather
models will struggle with total precipitation amounts as there
will be dry air initially that could cut amounts down, and then
some locations could get more snowfall thanks to dynamical
processes associated with overrunning mechanisms, and northwest
upslope regions like the Seeley-Swan region. As far as snow levels
are concerned, they will be much lower across western Montana as
modified Arctic air will be present, generally down to valleys.
There may be some locations in Idaho County that could have higher
snow levels towards 3000 feet.

The northwest flow pattern doesnt start to dry out until Tuesday
night or Wednesday morning. This could keep residual snow showers
around during this time period.

The pattern remains active through the rest of next week into next
weekend! The anomalously large upper level high pressure ridge
over the northeastern Pacific may get flattened a little bit. If
this occurs, then the Pacific Northwest and our region could be
recipients of a couple of subtropical moisture plumes aimed at us.
There will be a battleground for temperatures across the region as
any existing snowcover will help keep cold air in the valleys
(unless we get a strong wind gradient to wipe it all out). The
orientation of the upper jet will play a lot into who will get
wintry precipitation or not. Right now, the probabilities for snow
levels to be at valley level are highest across northwest Montana
next Friday into the weekend. Elsewhere there could be a mixture
of precipitation. Also with the colder week coming up, ground
temperatures will be falling to freezing or below down to 2500 to
3000 feet. This means that any rain that falls at night could turn
into freezing rain and black ice.


&&

.AVIATION...Arctic high pressure remains the dominant feature
across western Montana and north-central Idaho, generally
maintaining VFR conditions at primary terminals such as KGPI,
KBTM, KSMN and KHRF. A deck of low level clouds (ranging between
1400 to 3000 ft AGL) has filled into portions of the Missoula
(KMSO), Potomac and Mission valleys, locally obscuring terrain and
bringing MVFR conditions. The lower clouds are largely expected
to dissipate as an incoming weather system brings increasing
clouds aloft this afternoon and early evening.

Tonight into Sunday morning, a system moving in northwest flow
aloft will interact with the arctic boundary to bring an area of
enhanced snow showers, generally along and near the Idaho/western
Montana border from KMLP to KHRF to KBTM. Lowered ceilings and
visibility will obscure the terrain and will create MVFR to IFR
conditions for these locations between 30/0600z and 30/1200z.
Across northwest Montana, including KGPI, generally clear skies
are anticipated. Some valley fog may develop towards 30/0900z.

&&

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

$$