363
FXUS65 KMSO 191052
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
352 AM MST Sun Jan 19 2025

.DISCUSSION...

KEY MESSAGES:

-  Snow through this afternoon: Widespread 1 to 2 inches of light
   snow will create winter driving conditions, and reduced
   visibility across western Montana

-  Dangerously cold: A secondary Arctic surge will bring wind
   chills (-30F to -40F) along the Continental Divide, with
   subzero lows across much of Montana and single digits in north-
   central Idaho.


Light Snow This morning: Light snow has developed across
northwest Montana due to a weak disturbance moving southeast from
British Columbia. While moisture levels are limited, a deep
dendritic zone near the surface will allow for 1-2 inches of
light, fluffy snow across much of western Montana. Snow may also
affect higher elevations near the Bitterroot Divide in north-
central Idaho but is unlikely to reach as far west as the Camas
Prairie. Expect slick roads and reduced visibility due to the
snows light and powdery nature through this afternoon.

Arctic Air and Wind Chills: Another surge of arctic air is
forecast to move into northwest Montana by this afternoon,
spreading into the rest of western Montana and north-central Idaho
overnight into Monday morning. Along with plummeting
temperatures, a strong pressure gradient will bring gusty
northeast to east winds, leading to dangerously cold wind chills.
Wind gusts could reach up to 40 mph, especially in gaps and
channels aligned with the wind flow. By Monday morning, a much
colder air mass will settle over the region, with temperatures as
low as -20 to -30F in valleys near the Continental Divide, such
as Ovando, Butte, and Helmville. Winds are expected to diminish by
Monday morning as a strong 1050 mb high-pressure system
establishes itself along the Continental Divide, though drainage
winds may continue for areas such as the Missoula valley. Cold
weather advisories remain in effect through Monday for extreme
wind chills and frigid temperatures.

Lake-Effect Snow Monday and Tuesday: Lake-effect snow is likely
Monday into Tuesday. The significant temperature contrast between
the lake water (mid to upper 30s) and the air (low teens) will
create conditions favorable for heavy snowfall. Areas near the
southern and eastern shoreline of Flathead Lake could see several
inches of accumulation.

Temperature Trends and Future Arctic Air: Temperatures will
moderate slightly from Tuesday through Thursday, but this reprieve
will likely be brief. Forecast models suggest another surge of
arctic air could arrive around January 24-25 as a cutoff low-
pressure system develops. While there is some uncertainty
regarding the lows exact location, about 50% of models indicate
that moisture overrunning the cold air could result in moderate
snowfall for the region.

&&

.AVIATION...Light to moderate snow has begun across northwest
Montana this morning, and will spread through out the rest of
western Montana through the day today. Reduced visibility,
lowered ceilings, and mountain obscurations will be common with
the snow. Another push of Arctic air arrives in northwest Montana
late this morning (around 17-18Z at KGPI) with gusts of 25-35
kts. These easterly winds will impact the remainder of western
Montana this afternoon and evening but at diminished speeds of
15-25 kts, although a bit stronger near canyon gaps. Snow will
focus ahead of and along the arctic front in the afternoon and
evening, particularly the I-90 corridor into southwest Montana,
before decreasing significantly this evening and drier air
accompanies the cold.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Cold Weather Advisory from 5 PM this afternoon to 11 AM MST
     Monday for Bitterroot/Sapphire Mountains...
     Missoula/Bitterroot Valleys.

     Winter Weather Advisory until 2 PM MST this afternoon for
     Flathead/Mission Valleys...Kootenai/Cabinet Region...Lower
     Clark Fork Region.

     Cold Weather Advisory from 2 PM this afternoon to 11 AM MST
     Monday for Flathead/Mission Valleys...West Glacier Region.

     Winter Weather Advisory until 5 PM MST this afternoon for
     Bitterroot/Sapphire Mountains...Butte/Blackfoot Region...
     Missoula/Bitterroot Valleys...Potomac/Seeley Lake Region.

     Extreme Cold Warning from 5 PM this afternoon to 11 AM MST
     Monday for Butte/Blackfoot Region...Potomac/Seeley Lake
     Region.

ID...Cold Weather Advisory from 5 PM this afternoon to 11 AM MST
     Monday for Eastern Lemhi County...Western Lemhi County.

&&

$$