Sub-tropical moisture streamed over cold air already in place with abundant snowfall occurring.
Every event with a place to put it; 2 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
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.
Sub-tropical moisture streamed over cold air already in place with abundant snowfall occurring.
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 Feb 25, 2:40 AM PST, 7 hours 20 minutes earlier.
Area Forecast Discussion
National Weather Service Missoula MT
340 AM MST Thu Feb 25 2021
...HEAVY MOUNTAIN SNOW ACROSS THE CLEARWATER AND BITTERROOT
MOUNTAINS THROUGH FRIDAY...
.DISCUSSION...Regional radar and satellite imagery shows a potent
area of low pressure coming onshore in British Columbia early
this morning. The first wave of snowfall will arrive across north
central Idaho and northwest Montana by mid-morning. A strong mid-
level jet stream and a modest southwesterly oriented surface
pressure gradient will limit valley snowfall accumulations across
northwest and western Montana today. Confidence continues to
increase for strong south to southwesterly winds to develop across
the Camas Prairie in the vicinity of Grangeville by mid-morning.
Wind gusts between 40 and 50 mph will be common between 9 am and 2
pm PST today. Infrequent wind gusts up to 60 mph cannot be ruled
out. The strong winds will limit new snowfall accumulations for
these areas but will encourage blowing and drifting of the
existing snowpack. A winter storm warning may be warranted for
this area if widespread blowing and drifting of snow is observed
by mid- morning with the onset of strong winds.
A winter storm warning has been issued for the Clearwater
Mountains through Friday afternoon as high confidence exists for a
prolonged period of moderate to heavy snowfall and gusty westerly
winds. Storm total snowfall accumulations of one to two feet are
expected across the Clearwater Mountains, including: the US
Highway 12 corridor east of Lowell to Lolo Pass, Pierce, Elk
River, and Elk City, Idaho. Snowfall rates will increase Thursday
afternoon as a Pacific cold front passes through central Idaho.
High confidence exists for snowfall rates of at least one inch per
hour, particularly across Clearwater County, where low level
southwesterly winds will enhance orographic forcing. Widespread
moderate snowfall will continue Thursday night. Snowfall rates
will once again increase late Thursday night into Friday as a
secondary upper level disturbance moves into eastern Washington.
Forecast model soundings and cross-sections suggest strong
atmospheric ascent through the dendritic growth zone, a receipt
for heavy snow, across all of the north central Idaho. Travelers
should prepare for winter driving conditions across all of north
central Idaho Friday morning.
The atmosphere will destabilize Friday afternoon across the
Northern Rockies as the upper level trough axis moves overhead.
High resolution model guidance suggests numerous snow bands will
develop across north central Idaho and traverse across west-
central Montana. Areas along the south of the I-90 corridor in
western Montana will see impacts from these snow bands. Further
winter weather highlights may be needed on subsequent shifts to
address impacts related to these aforementioned bands for areas
such as the Bitterroot and Missoula valleys and the
Butte/Blackfoot region. Snow shower activity will generally
decrease Friday night, with mountain locations seeing the bulk of
ongoing accumulations.
Snow shower activity will once again increase across the Northern
Rockies Saturday. Confidence on valley snowfall accumulations
remain low at this time. One exception, will be across the West
Glacier region, where a shallow push of cold Canadian air will
move across the Continental Divide into the West Glacier region
Saturday, enhancing snow shower activity and potential
accumulations.
High pressure will briefly build across the Northern Rockies
Sunday ahead of the next potential weather maker. Model ensembles
continue to struggle with the evolution of the weather pattern
Monday into Tuesday next week. Two distinct scenarios continue to
be advertised. One solution favors a cool and active period as a
shortwave trough moves through the Pacific Northwest into the
area. The other solution splits the upper level trough off the
west coast and digs the trough into an upper level low off the
coast of California, leaving our region high and dry. Stay tuned!
&&
.AVIATION...A winter storm will impact the Northern Rockies later
this morning through Friday. The bulk of accumulating snow is
expected across north central Idaho, particularly across the
Clearwater Mountains. Gusty southwesterly to westerly winds up to
25 knots will develop areawide after 25/1800Z with the arrival of
a Pacific cold front. 50-60 knot winds at 10 kft MSL will lead to
mountain wave activity across much of the Northern Rockies. Strong
southerly winds up to 50 knots are possible in the vicinity of
KGIC between 25/1600Z and 25/2200Z.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT... Winter Weather Advisory from 8 AM this morning to 8 AM MST
Friday West Glacier Region.
Winter Weather Advisory from 8 AM this morning to 8 AM MST
Friday Kootenai/Cabinet Region.
Winter Weather Advisory from 8 AM this morning to 5 PM MST
Friday Lower Clark Fork Region.
ID...Winter Weather Advisory from 8 AM this morning to 4 PM PST
Friday Lower Hells Canyon/Salmon River Region.
Winter Storm Warning from 8 AM this morning to 4 PM PST Friday
Northern Clearwater Mountains.
Winter Storm Warning from 8 AM this morning to 4 PM PST Friday
Southern Clearwater Mountains.
Winter Weather Advisory from 8 AM this morning to 4 PM PST
Friday Orofino/Grangeville Region.
&&The national radar mosaic for the moment the first event began.
2 heavy snow. Local standard time, as filed.
Multiples periods of snow added up to 12-24 inches. Specific totals included 14 inches in Pierce and an estimated 24 inches at Elk River. Most of the impactful snow occurred above 3000 feet leading to difficult travel for much of the region.
General snow totals of 6-18 inches occurred with the heaviest totals at Lolo Pass with 21 inches. Chains were also required for towing units over Lolo Pass with snow covered roads all the way to Lowell.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Idaho in 2021Every state in 2021This day in weather historyWarnings in Idaho, February 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: 937906, 937907.