Winter Storm and Winter Weather in Idaho, February 11 to 12, 2021

Area Forecast Discussion
National Weather Service Missoula MT
221 PM MST Thu Feb 11 2021

.DISCUSSION...Today has been an intensely cold, windy day across
all of western Montana, and just as cold of a day (albeit not as
windy) across north central Idaho. Winds and bitterly cold
temperatures will remain a major threat the rest of the day and
overnight tonight as well, with some of the coldest readings
expected to occur Friday morning. Wind chills of -20 to -40
degrees will be common for most locations, however places along
the Continental Divide may continue to reach down to -50 degrees
or lower through Friday morning. We continue to stress the
importance of covering all exposed skin if you must be outside
during these conditions, and to make sure of the safety of those
around you, including pets and livestock.

The next impact to speak of will be the snowfall entering into
central Idaho from eastern Oregon and Washington through this
evening. Snowfall will be greatest around the Camas Prairie in
Idaho, as well as locations in and around the Clearwater mountains
and southern Bitterroot mountains. The Bitterroot valley itself,
from about Stevensville south through Darby, could see anywhere
from 2 to 5 inches tonight into Friday, with the higher end
falling across the southern half of the valley. Much less snow
(perhaps no more than an inch) is most likely for Missoula.

For the Camas Prairie region of north central Idaho, snow could
become moderate to heavy at times tonight and Friday morning. When
combined with increasing northerly winds, the threat for blowing
and drifting snow is high. Thus, we have issued a Winter Storm
Warning for the Camas Prairie due to the potential for heavy snow
combined with blowing snow. Locations such as Riggins, Shoup, and
southeastward into Salmon could see anywhere from 4 to 6 inches by
Friday afternoon. The higher terrain of central Idaho into west
central Montana could see up to 8 inches of new snowfall from this
system. Very little to no snow is expected north of I-90.

Another round of snow is expected across north central Idaho and
Lemhi County, Idaho Saturday as a Pacific storm system tracks
across eastern Oregon to south central Idaho. Pacific moisture
overrunning the arctic air will create a favorable scenario for
widespread snowfall, even at the lowest elevations. Modest
confidence exists for widespread swaths of 2 inches or more of
snowfall across Idaho and Lemhi Counties. The snowfall forecast
across western Montana south of the I-90 corridor remains highly
uncertain. Forecast models continue to struggle with track of the
low is it moves across south central Idaho. The low has been
trending a bit further south with time, which would reduce
snowfall potential across western Montana.

A upper level disturbance embedded within northwesterly flow will
promote a continuation of snow shower activity across north
central Idaho and Lemhi County Sunday. Minimal snowfall
accumulations are expected Sunday.

Widespread winter impacts will return across the Northern Rockies
Monday as another Pacific storm system tracks across eastern
Washington. Global models suggest a surface low could track across
north central Idaho and southwest Montana Monday afternoon into
Tuesday morning. An area of moderate snowfall is possible north
and west of the surface low, with the heaviest accumulations
likely targeting the Clearwater/Bitterroot mountains, and the I-90
and Highway 200 corridors from Missoula northwestward.

Model ensembles suggest an active winter weather pattern will
continue next week as a series of storm systems impact the
Northern Rockies. Stay tuned!

&&

.AVIATION...Strong arctic air and a dominating thermal boundary
will keep winds out of the north-northeast continuing. Most terminals,
particularly KMSO and KGPI, will see wind speeds of 15 to 25 mph
with gusts to 30 mph through the night into Friday. Bitterly cold
conditions will persist area-wide, even without the addition of
winds. At the same time, a moist weather system will move out of
eastern Oregon into central Idaho this evening after 12/00Z,
causing moderate to heavy snow for KGIC and KSMN through 12/18Z.
KBTM may see snow as well, though intensities will not be as
great. There is still some question as to how far north this area
of moisture will move, but for now, KMSO and KGPI will remain free
from snow impacts. Light snow may be possible by Friday morning at
KMSO, but again, confidence is low.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Wind Chill Warning until 2 PM MST Friday Butte/Blackfoot Region.

     Winter Weather Advisory from 5 PM this afternoon to 5 PM MST
     Friday Bitterroot/Sapphire Mountains.

     Wind Chill Warning until 2 PM MST Friday Bitterroot/Sapphire
     Mountains...Missoula/Bitterroot Valleys.

     Winter Weather Advisory from 5 PM this afternoon to 5 PM MST
     Friday Missoula/Bitterroot Valleys.

     Wind Chill Advisory until 2 PM MST Friday Kootenai/Cabinet
     Region...Lower Clark Fork Region.

     Wind Chill Warning until 2 PM MST Friday Flathead/Mission
     Valleys.

     Wind Chill Warning until 2 PM MST Friday Potomac/Seeley Lake
     Region...West Glacier Region.

ID...Winter Weather Advisory until 5 PM MST Friday Eastern Lemhi
     County...Western Lemhi County.

     Winter Weather Advisory until 4 PM PST Friday Lower Hells
     Canyon/Salmon River Region.

     Winter Storm Warning until 10 AM PST Friday Orofino/Grangeville
     Region.

     Winter Weather Advisory until 4 PM PST Friday Southern
     Clearwater Mountains.

&&