Ice Storm and Winter Storm in Montana, February 1, 2025

Area Forecast Discussion
National Weather Service Missoula MT
1020 PM MST Fri Jan 31 2025

.UPDATE...
Road conditions are quickly deteriorating around the Missoula
Valley and potentially into the Bitterroot. For that reason we
have upgraded the winter weather advisory to a warning due to ice.
Missoula Police Department has issued an emergency travel only
for the City of Missoula. Please if you have to travel this
evening check current road conditions via:

Montana - 511mt.net

Idaho - 511.idaho.gov

&&

.AVIATION...A significant and prolonged winter storm cycle is moving
into the region. Lowering clouds will continue to obscure more
terrain through the forecast timeframe. Ridgetop winds will
increase out of the west in excess of 30 knots through the rest of
today and into Saturday. Freezing rain and snow showers are
expected to move into the area out of the west slightly reducing
visibilities after 01/0000z. Potential for strong and gusty
westerly winds near the ground becomes likely through most of
Saturday with a potential for heavier banding snow showers and
even snow squall conditions through the afternoon. Wind gusts
could exceed 35 knots with the squalls.

&&

.PREV DISCUSSION... /ISSUED 228 PM MST Fri Jan 31 2025/

DISCUSSION...

KEY MESSAGES:

- Today-early Saturday: Valley freezing rain and heavy mountain
  snow creating hazardous travel conditions across Northern
  Rockies.

- Saturday morning-afternoon: Snow squall threat across west
  central and southwest Montana.

- Sunday-Monday: Arctic airmass will move west of the Continental
  Divide.

- Monday-Wednesday: Decent model agreement on significant snow
  accumulation event across western Montana valleys and also in
  the mountains/passes.

Precipitation has made it into north-central Idaho and far northwest
Montana. Interestingly, the mixed nature of precipitation this
morning over a short distance with snow near Yaak Hill and light
freezing rain at Bull Lake, of similar elevation and only 43 miles
apart. Inversions continue for some of the typical valleys along
the Highway 93 corridor but Hamilton did warm into the 40s about
midday. As precipitation gradually spreads eastward, light to
moderate freezing rain is a significant concern for many populated
areas of the Northern Rockies tonight. Keep in mind that even
with air temperatures slightly above freezing, cold ground
temperatures will encourage icy conditions as rain falls,
especially for secondary roads/sidewalks. Watch for highly
changeable road conditions with ice being the main threat in the
valleys and snowy for the passes.

A cold front passage on Saturday morning will help to lower snow levels
back to valley floors. Unstable conditions will lead to brief
heavy snow showers and gusty winds over 30 mph. Model soundings
and high resolution models support snow banding potential, mainly
from I-90 southward through late afternoon on Saturday. Watch for
brief intense snow, low visibility, and rapidly changing road
conditions under any snow bands that develop.

Little was noted in the way of change to the forecast from Sunday through
the middle of next week. Arctic air banks against the Divide
Saturday night, gradually spills into Northwest Montana Sunday,
then comes fully through the rest of western Montana on Sunday
night/Monday. Arctic air finally arrives in north-central Idaho
late Monday into Tuesday.

Periodic moisture will stream across the region Sunday into Monday morning
with several inches of snow for much of area. Monday night into
Tuesday will be a great opportunity for abundant snowfall as
subtropical moisture overruns the cold air in place. Run to run
the models are shifting where the next surge of moisture will be
positioned in relation to the Arctic boundary. This will greatly
affect which locations receive moderate to heavy snow with blowing
and drifting, currently the favored area for heavy snow is the
I-90 corridor, Missoula and Bitterroot valleys, and southwest MT.
Ensemble mean total liquid values range from 0.50 to 1.00" in
these areas which could equate to 1 to 2 feet of snow in the
valleys! Localized blizzard conditions are possible due to the
easterly arctic winds. Though hard to nail down where, freezing
rain continues to be a possibility from north- central Idaho south
and east to Lemhi County. The mountains could receive 1 to 3 feet
out of this system as well. Stay tuned as similar events in the
past have produced heavy valley snowfall where the moisture plume
and Arctic air coincide.

AVIATION...A significant and prolonged winter storm cycle is moving
into the region. Lowering clouds will continue to obscure more
terrain through the forecast timeframe. Ridgetop winds will
increase out of the west in excess of 30 knots through the rest of
today and into Saturday. Freezing rain and snow showers are
expected to move into the area out of the west slightly reducing
visibilities after 01/0000z. Potential for strong and gusty
westerly winds near the ground becomes likely through most of
Saturday with a potential for heavier banding snow showers and
even snow squall conditions through the afternoon. Wind gusts
could exceed 35 knots with the squalls.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Warning until 5 PM MST Saturday for
     Bitterroot/Sapphire Mountains.

     Winter Storm Watch from late Saturday night through late Tuesday
     night for Bitterroot/Sapphire Mountains.

     Winter Weather Advisory until 5 PM MST Saturday for
     Butte/Blackfoot Region...Potomac/Seeley Lake Region.

     Winter Storm Warning until 5 AM MST Saturday for
     Flathead/Mission Valleys...Kootenai/Cabinet Region...West
     Glacier Region.

     Winter Storm Watch from Sunday morning through Monday afternoon
     for Kootenai/Cabinet Region...West Glacier Region.

     Winter Storm Watch from Sunday morning through Tuesday evening
     for Flathead/Mission Valleys.

     Winter Storm Warning until 11 AM MST Saturday for Lower Clark
     Fork Region.

     Winter Storm Watch from Sunday morning through late Tuesday
     night for Butte/Blackfoot Region...Lower Clark Fork
     Region...Missoula/Bitterroot Valleys...Potomac/Seeley Lake
     Region.

     Winter Storm Warning until 5 PM MST Saturday for
     Missoula/Bitterroot Valleys.

ID...Winter Storm Warning until 4 PM PST Saturday for Northern
     Clearwater Mountains...Southern Clearwater Mountains.

     Winter Storm Watch from late Saturday night through late Tuesday
     night for Northern Clearwater Mountains...Southern
     Clearwater Mountains.

     Winter Weather Advisory until 10 AM PST Saturday for
     Orofino/Grangeville Region.

     Winter Weather Advisory until 5 PM MST Saturday for Eastern
     Lemhi County...Western Lemhi County.

&&