598
FXUS65 KMSO 182102
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
302 PM MDT Sat Oct 18 2025

.DISCUSSION...

KEY MESSAGES:

- Strong south winds on Flathead Lake tomorrow will cause choppy
  conditions for boaters.

- An atmospheric river will arrive in the region tonight and last
  through early next week causing heavy rain in the mountains.

- Snow levels will fall near the end of the atmospheric river
  event causing several inches of snow accumulation in the
  mountains just after receiving around an inch of rain.

- A warm break from the moisture for most of the week, and then
  another atmospheric river is possible around next Saturday.

Strong southerly winds tomorrow will cause choppy conditions on
area lakes, especially Flathead Lake tomorrow where 2 to 3 foot
waves are expected in the afternoon. This lake wind event is a
little unusual because of the timing, we expect winds to start
increasing in the morning and remain high through the day.

An atmospheric river moving into the region this evening will
cause snow levels to rise with moderate to heavy rain rates
expected in the mountains. The mountains of central Idaho and
northwest Montana will be hardest hit, including the Bitterroot
mountains in western Montana. Storm total liquid equivalent
precipitation amounts will range for around 0.75 inches to over
2.0 inches in the mountains by Tuesday morning. Most of that will
fall as rain.

But Sunday the snow levels start to fall, and the snow to liquid
ratios start to rise by late Sunday. Winter weather advisories
have been issued for many mountain locations from Sunday night
through Monday morning as several inches of snow are expected
above 5,000 ft. With most back country roads on public lands still
accessible by the public, this is cause for concern for those who
might be using them. Be prepared for very wet, cold, and windy
conditions. If you`re going up to higher elevations, be prepared
for several inches of snow. Snow accumulations by Monday morning
will be around 2-5 inches around 5,000 to 6,000 feet and upwards
of 7 to 12 inches is possible above 6,000 ft. So it will start
with moderate to heavy rain for a day or so, then transition to
snow and accumulate a few to several inches, all while the wind is
blowing 25-35 mph. These are ideal conditions for hypothermia.

Through the middle of the week weather conditions will moderate
with a ridge building over the region. Then, another atmospheric
river is becoming more likely for next weekend. Current forecasts
show that for northwest Montana, but it`s about a week out. Stay
tuned!



&&

.AVIATION...Expect increasing clouds this afternoon as an
atmospheric river moves into the region. By morning, rain will
have started at most area terminals with VFR to MVFR restrictions
expected due to low ceilings and mist. Snow levels will be rising,
so no snow impacts are expected at any terminals through Sunday.
There is a low probability (less than 10 percent) for some
freezing rain to briefly affect terminal KGPI tomorrow morning,
though we expect the increasing cloud cover and winds to prevent
the temperatures there from reaching freezing which is why the
probability is so low. If, however, it does clear out for a few
hours with lighter winds, it could set up a freezing rain scenario
for tomorrow morning when the rain arrives.


&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory from 9 PM Sunday to 9 AM MDT Monday for
     Bitterroot/Sapphire Mountains...Potomac/Seeley Lake
     Region...West Glacier Region.

     Lake Wind Advisory from 6 AM to 9 PM MDT Sunday for
     Flathead/Mission Valleys.

ID...Winter Weather Advisory from 8 PM Sunday to 8 AM PDT Monday for
     Southern Clearwater Mountains.

&&

$$