Heavy snow fell ahead of a warm front on the 17th, especially across Northwest Montana. An Arctic front brought strong winds and additional snow late on the 17th into the 18th across all of western Montana.
Every event with a place to put it; 8 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.
Heavy snow fell ahead of a warm front on the 17th, especially across Northwest Montana. An Arctic front brought strong winds and additional snow late on the 17th into the 18th across all of western Montana.
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 17, 3:49 AM MST, 7 hours 11 minutes earlier.
Area Forecast Discussion
National Weather Service Missoula MT
349 AM MST Sat Feb 17 2018
.DISCUSSION...
The next enhancement of light to moderate snow has already begun
shifting into north-central Idaho and northwest/west-central
Montana early this morning. This snow is expected to intensify in
northwest Montana today, particularly north of I-90 where snow
levels should stay at/near valley floors. Snow will become
moderate to heavy at times, leading to periods of significantly
reduced visibility. Generally south of I-90, warmer air is
forecast to spread into the area today. This should transition
precip for valleys into a dense rain/snow mix or all rain
temporarily this afternoon, interrupting snowfall accumulations.
Snow levels could raise as high as 3500-4500 feet by this
afternoon/evening, which may even briefly reach as far north as
the Mission/southern Flathead Valleys. This warm air will quickly
be shunted, however, as colder Pacific air drops in from the
northwest later this evening.
At the same time as the Pacific front, an arctic front will be
pushing into Flathead County tonight. North and east winds will
rapidly increase and create blizzard-like conditions for the US-2
corridor and into the northern Flathead Valley via Badrock Canyon.
Travel will be difficult to impossible from blowing and drifting
snow as wind gusts could exceed 40-50 mph at times. Wind damage to
trees and powerlines is also possible in these locations. This
arctic air mass will continue to push westward into the rest of
western Montana by Sunday morning, creating strong gusty winds and
difficult conditions through the US-12/MT-200/I-90 corridors into
west-central and southwest Montana. Moderate to heavy snowfall
will be enhanced by these collision of airmasses overnight and
Sunday morning. Snow totals, especially for the terrain and
northwest Montana, are expected to be significant for the next 48
hour period. Please refer to the Winter Storm Warnings for more
details.
The snow will continue to shift southward and decrease throughout
the day on Sunday as the arctic air settles into the region.
Temperatures will drop dramatically behind the arctic front. Most
valley locations of western Montana will be in the single digits
to below zero by Monday morning. While the lower valleys of Idaho
remain in the teens and 20s. Minimal warming is anticipated for
Monday as maximum temperatures appear to be around 20 degrees
below normal for this time of year.
The Northern Rockies remain under northwesterly flow aloft which
will keep the arctic air from modifying. The region appears to be
cold and fairly dry through the mid part of next week. A
disturbance is expected to drop into the region by
Wednesday/Thursday time frame, but the models diverge on the path
of the system. Active weather is anticipated through at the least
the weekend.
&&
.AVIATION...Light to moderate snow will begin to spread across the
northern Rockies beginning this morning, and intensifying later
today. Significant moderate to heavy snowfall accumulations will
be favored generally north of I-90 today into Sunday. KMSO, KSMN,
and KBTM are expected to transition to a rain/snow mix or all
rain during this afternoon/evening period before becoming all snow
once again tonight.
Winds will initially be gusting from the west and south today. An
arctic front will begin pushing into Flathead County by late this
afternoon/evening, and gusty north and east winds of 25-35 kts
will begin for KGPI generally after 18/0000Z. The arctic front
will reach the rest of western Montana by early Sunday morning.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory until 5 AM MST early this morning
Butte/Blackfoot Region.
Winter Weather Advisory from 11 AM this morning to 5 PM MST this
afternoon Butte/Blackfoot Region.
Winter Storm Warning from 5 PM this afternoon to 5 PM MST Sunday
Butte/Blackfoot Region...Potomac/Seeley Lake Region.
Winter Weather Advisory until 5 PM MST this afternoon
Potomac/Seeley Lake Region.
Winter Weather Advisory until 11 AM MST this morning
Bitterroot/Sapphire Mountains.
Winter Storm Warning from 11 AM this morning to 5 PM MST Sunday
Bitterroot/Sapphire Mountains.
Winter Weather Advisory until 11 AM MST this morning
Missoula/Bitterroot Valleys.
Winter Storm Watch from 11 AM MST this morning through Sunday
afternoon Missoula/Bitterroot Valleys.
Winter Weather Advisory until 11 AM MST this morning
Flathead/Mission Valleys...Kootenai/Cabinet Region...Lower
Clark Fork Region...West Glacier Region.
Winter Storm Warning from 11 AM this morning to 5 PM MST Sunday
Lower Clark Fork Region.
Winter Storm Warning from 11 AM this morning to 5 PM MST Sunday
Flathead/Mission Valleys.
Winter Storm Warning from 11 AM this morning to 5 PM MST Sunday
West Glacier Region.
Winter Storm Warning from 11 AM this morning to 5 PM MST Sunday
Kootenai/Cabinet Region.
ID...Winter Weather Advisory from 5 PM this afternoon to 5 PM MST
Sunday Eastern Lemhi County...Western Lemhi County.
Winter Weather Advisory until 10 AM PST this morning Northern
Clearwater Mountains...Southern Clearwater Mountains.
Winter Storm Warning from 10 AM this morning to 4 AM PST Sunday
Northern Clearwater Mountains...Southern Clearwater
Mountains.
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
747 AM MST SAT FEB 17 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0730 AM SNOW 2 WNW STEVENSVILLE 46.52N 114.13W
02/17/2018 E6.0 INCH RAVALLI MT TRAINED SPOTTER
OVERNIGHT SNOWFALL.
&&The national radar mosaic for the moment the first event began.
7 winter storm, 1 heavy snow. Local standard time, as filed.
Heavy snow on the 17th was followed by snow and gusty winds late on the 17th into the 18th leading to periods of severe driving conditions. Snow amounts of 8 to 12 inches were common with 18 inches at Marion.
Heavy snow on the 17th with rates of 1 to 2 inches per hour were followed by strong winds the evening of the 17th into 18th. Snowfall totals of 12 to 18 inches were common along with wind gust of 35 to 45 mph. Severe driving conditions were widespread.
Periods of severe driving conditions occurred much of the 17th into the 18th due to heavy snow with some gusty winds. Twenty-four hour snow amounts included 26 inches at Lookout Pass and 22 inches just west of Trout Creek.
Severe driving conditions with chains required were reported on U.S. Highway 2 from Columbia Falls to Marias Pass due to snow as well as blowing and drifting of snow. Essex reported 18 inches of new snow.
Heavy bursts of snow with amounts around 12 inches were common leading to difficult travel over area mountain passes. The highway department noted that it was difficult to keep up with snow rates near Lolo Pass late on the 17th.
Snow, blowing snow, and a flash freeze led to severe driving conditions late on the 17th into the 18th. Wind gusts of 30 to 40 mph on the morning of the 18th combined with snow to produce greatly reduced visibilities.
Severe driving conditions were observed on major travel routes due to snow and blowing snow. Wind gusts of 50 to 60 mph were common creating localized ground blizzard conditions.
Numerous slide off crashes and jackknifed semi trucks occurred on Interstate 90 due to snow and blowing snow. Widespread snowfall amounts of 8 to 12 inches were common with wind gusts of 35 to 45 mph.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2018Every state in 2018This day in weather historyWarnings in Montana, February 2018
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: 732650, 732653, 732655, 732652, 733104, 732656, 732659, 732660.