060
FXUS65 KMSO 071846
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
1246 PM MDT Tue Oct 7 2025

.DISCUSSION...

KEY MESSAGES:

- A cold, wet system will bring rain and mountain snow Saturday.

- Late Saturday or Sunday, snow levels will drop causing a
  transition to snow.

- A lot of uncertainty remains about the manner in which the
  trough that causes the wintry weather will exit the region.

A deep trough approaching the U.S. West Coast will cause
increasing breezes tomorrow and Thursday, with a wet an snowy
weekend ahead. Southerly flow ahead of the trough will help bring
some warm, moist air with tropical origins into the region Friday
night and Saturday. This will cause snow levels to rise above
9,000 or 10,000 ft elevation Friday. Models still disagree on the
timing, but snow levels will start to fall again on Saturday after
it starts raining. By Sunday morning, snow levels are forecast to
drop below 5,000 ft all across western Montana and central Idaho.

Median snow forecasts for Monday morning include 6-10 inches of
storm total snow in the Mission, Swan, and Whitefish mountains
with around a foot in the higher elevations of Glacier National
Park. Further south in the Bitterroot Mountains, expect 4-8 inches
of new snow including Lookout and Lost Trail passes. The median
forecast for Lolo Pass is 2-3 inches. High end forecasts (90th
percentile) have 18-24 inches in the mountains of northwest
Montana and around 12 inches in the Bitteroot mountains for storm
total snows.

This is the first winter system of the year that has the potential
to impact travel over mountain passes. Lookout, Lost Trail, Lolo,
and Marias passes are expected to be the hardest hit, but Rogers,
and MacDonald passes also have a chance (10-20%) of picking up a
few inches of snow. Current forecasts for Homestake Pass show a
few tenths of an inch to 2 inches of snow. A major concern with
snow on the passes this time of year is melting and refreezing,
causing very icy conditions. Even if the snow is melting on the
roads, once the sun goes down or the temperature drops just enough
the roads can become icy in a matter of minutes. If you`re
traveling this weekend or early next week, be prepared for winter
conditions in the mountains.

While ensembles agree well on the arrival of the trough and colder
air, there is considerable disagreement on how it exits the region
early to mid next week. Once it starts to move out of the region,
it will start interacting more strongly with any tropical systems
in the Atlantic basin, and currently there`s quite a bit of
uncertainty in those long term forecasts, which translates to a
lot of uncertainty for mid next week.


&&

.AVIATION...A ridge over the region starts to flatten out and
southwest flow becomes established over the region as a trough
digs off the U.S. West Coast. Impacts to aviation will be nil as
only some high cloud starts to increase over the region with
increased breeziness Wednesday. Friday and this weekend will bring
a big change as that digging trough moves onshore.

&&

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

$$