551
FXUS65 KMSO 062126
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
226 PM MST Sat Dec 6 2025

.DISCUSSION...

KEY MESSAGES:

- Heavy mountain snow, along with a wintry mix in the valleys
  will make for difficult travel conditions today

- Significant rain and high elevation snow Monday through
  Wednesday may lead to hydrologic issues

Snow levels continue to be the most significant challenge to the
forecast for the next 24 to 48 hours. Confidence is high that
precipitation will continue to stream into the Northern Rockies
with pulses of heavier precipitation rates at times. Confidence is
high that the mountains will receive some significant snow with
the mountain passes along the Montana/Idaho border having periods
of moderate impacts for the next 24 to 48 hours. Confidence starts
to waver on which valleys will completely mix out so the
precipitation type will remain rain throughout the event. At this
moment, Missoula valley, Seeley/Swan valley and the majority of
the valleys of Lincoln/Flathead counties are having a difficult
time mixing out, so temperatures have been hovering in the low to
mid 30s throughout the day. While the other valleys have
experienced temperatures more in the upper 30s to mid 40s today.
This trapped colder air in the valleys will allow for the
potential for the precipitation type to remain snow, especially
during the overnight hours. The valleys that do remain snow could
have periods of moderate impacts to the roads due to snow
accumulation and/or patchy ice due to refreeze of wet surfaces.

Late Monday into Tuesday the first pulse of moisture from the
atmospheric river will push into the Northern Rockies causing snow
levels to rise with a range of around 5000 feet across northwest
Montana to 7000 feet over Lemhi county. The models are in fairly
good agreement with this snow level range. The higher mountains of
the Northern Rockies should expect up to 18 inches of new snow,
while the mountain passes will struggle to get a couple of inches
of new snow. North central Idaho into northwest Montana will
receive a significant amount of rainfall from this feature with
totals appearing to range from 1 to 2 inches by Tuesday afternoon.
The models are showing a gusty westerly winds pushing into the
region which will cause downsloping effects in the broader valleys
and wind prone areas. The Camas Prairie of Idaho, Hwy 93 corridor
and Lemhi county into southwest Montana are expected to receive
around 0.10" up to 0.50" of rainfall. The precipitation is
anticipated to taper off Tuesday afternoon and evening.

The second pulse of significant moisture impacts the Northern
Rockies Tuesday night into Wednesday evening. The models have a
considerable spread in potential snow levels for this event, but
the overall solutions is for snow levels to be above most valleys
locations. The current snow level mean during this event is around
4000 feet in northwest Montana to 7000 feet over Lemhi county. The
mountains will once again get a foot or two of new snow. The winds
do not appear to be as strong during so less downsloping effects
in the valleys, so rainfall ranges in the valleys appear to be
between 0.50" to 2.00". Once again Idaho/Clearwater counties
appear to have the best potential for significant rainfall
accumulation.

The combination of two hefty rainfall along with the potential for
snow melt of the lower elevations could bring hydrological issues
to Idaho/Clearwater county up into northwest Montana. Some impacts
that could be experienced is ponding and flooding of low lying
areas that have poor drainage, rapid rises of creeks and streams
and rock/mud slides.

The latter part of the week appears to remain quite active as
cooler air begins to infiltrate the region with a 25% chance of
an arctic airmass moving into northwest Montana by Friday.


&&

.AVIATION...Northwesterly flow continues over the Northern Rockies
causing precipitation and clouds over the majority of the region.
Snow levels have generally risen to around 4000 feet, but some
valleys have not completely mixed out so snow down to valley
floors will be an issue. KGPI and KMSO have the potential of
experience some snow over the next 24 hours as pulse of showers
move through the region. The higher terrain across north central
Idaho into west central and northwest Montana will be mostly
obscured by low clouds and snow. KHRF will be dealing with gusty
south winds along with periods of reduced visibility due to rain.
KBTM and KSMN will mainly have vicinity showers. Another concern
will be the valleys that do not mix out the development of fog and
low stratus will be an issue.

&&

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

$$