838
FXUS65 KMSO 071021
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
321 AM MST Sun Dec 7 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

Banded showers continue this morning, bringing snow to mountain
passes, and a wintry mix of rain, snow and sleet to valleys.
Near-freezing surface temperatures will maintain variable road
conditions, with rapid changes from wet to icy surfaces likely
over short distances through mid morning.

Increasing southwest-to-west winds today should scour out cold
pools in persistent inversion valleys (e.g., Missoula, Kalispell),
allowing temperatures to modify into the upper 30s. Precipitation
will largely transition to orographic showers by late morning
before reinvigorating this afternoon and evening. While valleys
remain warm enough for rain, mountain passes, specifically Lolo,
Lost Trail, and Marias, will accumulate an additional 2 to 6
inches of snow (25th to 75th percentile), presenting travel
difficulties.

On Monday, the first big surge of an incoming atmospheric river
will spread anomalous amounts of moisture and mild air into the
region. Snow levels will rise significantly through the day,
peaking Monday night between 6000 to 7000 feet. Heavy rainfall is
expected below this elevation, maximizing over North Central Idaho
and Northwest Montana. Strong westerly flow aloft will induce
distinct shadowing effects, limiting QPF somewhat in the valleys
of Western Montana.

Forecast models continue to show a brief lull in precipitation
rates Tuesday afternoon before increasing once again Tuesday
evening through Wednesday night. With this second wave of moisture
there is quite a bit of uncertainty in snow levels, with some
forecast models showing colder air settling into the region from
the north and lowering snow levels potentially as low as 3500-4000
feet. This colder scenario (~25% chance) would bring potential
for moderate to heavy snow into higher valleys and travel
corridors, especially in northwest Montana.

All in all, the 72 hr precipitation forecast (ending 5am Thursday)
shows impressive totals, favoring north central Idaho and the
higher terrain of northwest Montana. The 72-hour QPF (ending 12Z
Thursday) indicates significant hydrologic input. Totals range
from 0.50 to 2.00 inches in shadowed valleys and 2.50 to 5.00
inches (10th to 90th percentile) in North Central Idaho and the
Northwest Montana terrain. The coincidence of heavy rain and
melting low-elevation snowpack increases the risk of rapid rises
on creeks and streams, ponding in poor drainage areas, and
rock/mudslides. In addition, though not as visible to most,
hazardous conditions will be in place in the backcountry above
6000 feet due to heavy snow and strong winds causing blowing snow
and low visibility.

&&

.AVIATION...Banded precipitation continues to produce widespread
mountain obscurations across the Northern Rockies this morning.
Valley terminals (KMSO, KGPI) are experiencing fluctuations
between VFR and MVFR conditions due to visibility reductions in
rain, snow, and sleet. A brief lull in precipitation is
anticipated late morning, potentially allowing ceilings to lift to
low-end VFR or high-MVFR. However, dynamic forcing returns after
21Z, lowering ceilings back to MVFR with widespread rain for the
valleys and snow in the terrain into the overnight hours.
Increasing winds aloft are expected this evening, with ridge top
winds approaching 45 kts. Turbulence and low level wind shear will
become a concern.

&&

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

$$