350
FXUS65 KMSO 170925
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
225 AM MST Wed Dec 17 2025

.DISCUSSION...

KEY MESSAGES:

 - Strong Cold Front today: An extreme cold front will sweep
   across the region this morning. Expect a rapid transition from
   rain to snow, and damaging winds with gusts of 40-60 mph in
   valleys (higher in mountains).

 - Snow Thursday and Friday: Following the front, cooler and
   unsettled weather will prevail for the remainder of the week,
   with snow levels dropping to valley floors at times and periods
   of mountain snow affecting travel.

 - Mountain snow Saturday

Satellite imagery early this morning is showing a low pressure
circulation moving into central British Columbia. This circulation
is pushing a strong cold front from west to east south of the low
pressure center. The front will strengthen as it moves through
the Pacific Northwest and arrives in the Northern Rockies this
morning. The primary impact from this feature, well-advertised
over the last several days, will be strong, damaging winds. Timing
for arrival will be about 5am PST in Idaho and Clearwater
counties, moving east to western Montana by about 7am MST, and
becoming widespread throughout the Northern Rockies including
southwest Montana and Lemhi County by about 9am MST. Southerly
winds early in the event will turn westerly with the frontal
passage. Westerly gusts of 50 mph will be widespread. High
resolution ensemble models indicate a 50 to 90 percent chance for
gusts of this magnitude across most valleys in the Northern
Rockies. In the higher terrain such as the Continental Divide and
the Bitterroot crest, there will be about a 50 percent chance of
exceeding 70 mph. A secondary threat today will be the transition
from rain to snow behind the front. Snow accumulation will favor
northwest Montana, especially eastern Flathead County. Marias Pass
will see about 6 to 12 inches of snow by tonight. A Winter Storm
Warning is in effect for the Glacier Park region due to the
combination of high winds and snow, while the remainder of the
Northern Rockies will be under a High Wind Warning through today.

Moving on past today, enough cold air holds on through Thursday
for snow accumulation in the higher terrain by Friday morning.
Moisture is still supplied from the Pacific Ocean by an upper
level jet positioned over the Northern Rockies. Cool temperatures
will keep snow levels low enough for valley snow through Thursday,
while forcing for ascent will come from the terrain with the
exception of some weak overrunning of Pacific moisture over
residual cold air in the valleys. Accumulations over mountain
passes such as Lolo, Lookout, Marias, and Lost Trail will be in
the 5 to 10 inch range. A Winter Storm Watch is in effect for the
Clearwater, Bitterroot, and Sapphire ranges for Thursday and
Friday.

Snow levels rise again on Friday afternoon, then come back down to
valley floors for Saturday. The mountains hang onto snow into
Saturday as the Clearwaters and Bitterroots are favored for
another several inches of snow by Saturday morning. The next
period of interest for precipitation will be Sunday into Monday,
though model agreement is still uncertain.

&&

.AVIATION... Wind will be the primary impact to aviation over the
next 24 hours. A potent cold front is approaching the Northern
Rockies from the west. Southerly winds early will turn westerly
behind the front, arriving in north-central Idaho by about
17/1300Z and western Montana by about 17/1400Z. Expect gusts of 40
to 50 knots near the ground, 60 knots over the terrain. Low-level
windshear will also develop early this morning and persist
throughout today. Snow will obscure terrain, while rain will turn
to snow by about midday at all terminals. Precipitation,
including blowing snow, will produce reductions in visibility.


&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Watch from late tonight through late Friday night
     for Bitterroot/Sapphire Mountains.

     High Wind Warning until 5 PM MST this afternoon for
     Bitterroot/Sapphire Mountains...Flathead/Mission Valleys...
     Kootenai/Cabinet Region...Lower Clark Fork Region...
     Missoula/Bitterroot Valleys.

     Winter Storm Warning until 11 PM MST this evening for West
     Glacier Region.

     High Wind Warning until 8 PM MST this evening for
     Butte/Blackfoot Region...Potomac/Seeley Lake Region.

ID...High Wind Warning until 2 PM MST /1 PM PST/ this afternoon for
     Eastern Lemhi County...Lower Hells Canyon/Salmon River
     Region...Northern Clearwater Mountains...
     Orofino/Grangeville Region...Southern Clearwater
     Mountains...Western Lemhi County.

     Winter Storm Watch from late tonight through late Friday night
     for Southern Clearwater Mountains.

&&

$$