An Arctic cold front moved over the Divide, leading to heavy snow and areas of blowing snow.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS MSO wrote it up.
An Arctic cold front moved over the Divide, leading to heavy snow and areas of blowing snow.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Missoula, MT wrote its last area forecast discussion before the first event at Dec 24, 3:01 PM MST, 1 hour 59 minutes earlier.
Area Forecast Discussion
National Weather Service Missoula MT
301 PM MST Fri Dec 24 2021
.DISCUSSION...Low pressure spinning along the coast of Washington
state will slowly move eastward over the course of the upcoming
holiday weekend. As it does, it will send moisture into the
Northern Rockies under southwesterly flow. This moisture feed will
keep a chance for snow in the forecast throughout the region.
More notably, an arctic cold front will breach the Continental
Divide this evening in the Glacier Park region. As the front
interacts with the warmer, moist air from the southwest, heavy
snow will become likely over eastern Flathead County including
Highway 2 from Hungry Horse to Marias Pass, Essex, West Glacier,
and Polebridge. These locations will be under a Winter Storm
Warning this evening through Christmas morning.
The arctic airmass will continue to move west and south on Sunday,
infiltrating the valleys of western Montana. Meanwhile, a low
pressure system to the west of the Northern Rockies will sink
southward over time and eject weak waves of moisture toward the
Continental Divide. The juxtaposition of the arctic air and the
waves of moisture may present a profound winter weather impact for
portions of west central and northwest Montana throughout Sunday.
There is still a great deal of model and ensemble spread covering
the position of the arctic front and just how much moisture will be
available. Thus, there are Winter Storm Watches in effect on
Sunday, mainly targeting where the arctic air and relatively warm
moisture cross.
The low pressure system mentioned for Sunday appears to finally move
south of the Northern Rockies and over the Snake River Plain on
Monday, likely ending the widespread snow impact for the region.
However, near zero and sub-zero air will continue to move west of
the Continental Divide through the middle of next week. Over time,
the worst-case temperature expectations have moderated a bit,
however it's still pretty cold (and fitting for the climatologically
coldest week of the year for many locales). One tempering input to
the cold will be a continuation of weak storm systems moving over
the Northern Rockies throughout next week.
Similar to previous forecasts, temperatures are expected to begin a
warming trend across the Northern Rockies by the end of next week. A
weak snow event may be the catalyst to begin this relative warming,
with at least several inches of snowfall across the northern
Clearwater Mountains in Idaho and along the Montana-Idaho border.
&&
.AVIATION...Winter weather including gusty northeast winds and
snow will arrive at KGPI this evening around 25/0200Z. Gusty winds
will continue through tonight and into Christmas Day. Northwest
Montana will experience decreased visibility and ceilings
overnight. Snow will also affect KMSO overnight by around
25/0600Z. Intermittent snow will continue throughout Christmas Day
and will obscure terrain over all ranges of the Northern Rockies.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Watch from late Saturday night through Sunday
evening Butte/Blackfoot Region.
Winter Weather Advisory until 11 AM MST Saturday Lower Clark
Fork Region.
Winter Storm Watch from late Saturday night through Sunday
evening Flathead/Mission Valleys.
Winter Weather Advisory until 5 PM MST this afternoon West
Glacier Region.
Winter Storm Warning until 11 AM MST Saturday West Glacier
Region.
Winter Weather Advisory until 11 AM MST Saturday
Kootenai/Cabinet Region.
Winter Storm Watch from late Saturday night through Sunday
evening Kootenai/Cabinet Region.
ID...None.
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
1237 PM MST FRI DEC 24 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0927 AM SNOW PIERCE 46.49N 115.80W
12/24/2021 M2.2 INCH CLEARWATER ID CO-OP OBSERVER
CO-OP OBSERVER STATION PIRI1 PIERCE.
&&The national radar mosaic for the moment the first event began.
1 winter weather, 1 winter storm. Local standard time, as filed.
A series of heavy snow showers with snowfall rates around one inch per hour impacted Lookout Pass Christmas Eve. A crash closed I-90 westbound on the Idaho side of Lookout Pass.
A period of heavy snow was observed across the West Glacier region Christmas Eve, with snowfall rates around two inches per hour. Temperatures quickly dropped into the single digits as an arctic front moved over the Divide early Christmas morning. Snow and blowing snow was observed on US 2, with wind chills of -10 to -20.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2021Every state in 2021This day in weather historyWarnings in Montana, December 2021
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 997623, 997624.