A west to east oriented 150 knot upper level jet moves south of the area while heavy snow fell across sections of northwest Montana and also by the Continental Divide. Light to moderate snow accumulations fell across valleys of the remainder of west-central Montana before and during the morning commute.
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.
A west to east oriented 150 knot upper level jet moves south of the area while heavy snow fell across sections of northwest Montana and also by the Continental Divide. Light to moderate snow accumulations fell across valleys of the remainder of west-central Montana before and during the morning commute.
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 16, 3:04 PM MST, 4 hours 31 minutes earlier.
Area Forecast Discussion
National Weather Service Missoula MT
304 PM MST Sun Dec 16 2012
...SIGNIFICANT SNOW AND WIND FOR PORTIONS OF THE NORTHERN ROCKIES
TONIGHT THROUGH MONDAY EVENING...
.DISCUSSION...
A vigorous Pacific storm system will bring wind and snow to the
Northern Rockies tonight through Monday evening. Snow and wind
will combine to limit visibility and create hazardous driving
conditions. All area mountain passes will experience at least some
snow accumulation, blowing snow, drifting snow, and visibility
down to one quarter mile or less at times. The most significant
impacts will be found over Lookout and Marias Passes, where wind
gusts to 50 mph combined with heavy snowfall may create nearly
impossible travel conditions at times, particularly during Monday
morning. Snow will also be significant for lower elevations of
northwest Montana, with locations such as Libby and Yaak expected
to receive 6 to 12 inches of snow. Wind gusts to 50 mph and minor
snow accumulations are anticipated over the Camas Prairie of
Idaho, particularly as the surface cold front passes through
during the Monday morning hours. Even small amounts of snow on the
Camas Prairie will likely melt and refreeze, resulting in
dangerous black ice. High profile vehicles traveling on Highway 95
will be especially susceptible to losing control with the strong
crosswinds and an icy road surface. Unlike some wind events that
are confined to Grangeville and vicinity, this particular wind
event will occur across the entire region. Winter weather
highlights are in effect for nearly all locations across the north
central Idaho and western Montana with the exception of the
Missoula and Bitterroot Valleys. Confidence remains fairly low
that either valley will receive appreciable snow due to strong
westerly winds providing a dry, downsloping flow. Winter weather
higlights for Missoula and Bitterroot Valleys may be addressed
later.
Light snow showers will remain during Tuesday, however the
significant accumulations will be past. Temperatures will struggle
to reach freezing at most locations on Tuesday afternoon. Tuesday
appears to be an intermission within a larger storm cycle
anticipated to continue through next weekend.
Wednesday through Saturday...A southwest flow will develop over
the Northern Rockies as a large trough of low pressure digs south
along the west coast. Within this flow will be embedded a number
of shortwaves that will keep the chance of rain and snow over the
region through the weekend. Uncertainty exists this weekend when
the main trough moves inland. Its exact track is still in question
which leaves little confidence in this weekend's forecast.
&&
.AVIATION...Snow showers through Idaho and western Montana will
obscure terrain and reduce ceilings and visibilities at times this
afternoon. A warm front associated with the next weather system is
already spreading clouds and precipitation through much of the
Pacific Northwest. This front will move into Idaho and western
Montana this evening. Snow will begin in Idaho and in much of
western Montana by late this evening. Model guidance show that
moisture will continue to increase overnight, and very low
ceilings and visibilities are expected under widespread snow. Gusty
winds will also develop in the terrain and through the Camas
Prairie tonight. Very low visibilities are expected in the
wind and snow. Current timing has the cold front to pass Monday
morning and the surface low to pass through northwest Montana
during the same time. Gusty winds will develop region-wide with the
cold front and intense snow showers are possible. The surface low
will provide the focus for moderate and even heavy snow through
northwest Montana through Monday. Snow showers will continue
through Monday night with obscured terrain likely.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY from 2 AM to 11 PM MST Monday
Bitterroot/Sapphire Mountains...Butte/Blackfoot Region.
WINTER STORM WARNING from 11 PM this evening to 11 PM MST Monday
Lower Clark Fork Region.
WINTER WEATHER ADVISORY from 2 AM to 11 PM MST Monday
Flathead/Mission Valleys...Potomac/Seeley Lake Region.
WINTER STORM WARNING from 2 AM to 11 PM MST Monday West Glacier
Region.
WINTER STORM WARNING from 11 PM this evening to 11 PM MST Monday
Kootenai/Cabinet Region.
ID...WINTER WEATHER ADVISORY from 2 AM to 11 PM MST Monday Eastern
Lemhi County...Western Lemhi County.
WINTER WEATHER ADVISORY from 10 PM this evening to 10 PM PST
Monday Lower Hells Canyon/Salmon River Region...Northern
Clearwater Mountains...Orofino/Grangeville Region...
Southern Clearwater Mountains.
&&
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Kitsmiller/Zumpfe/LoeffelbeinThe national radar mosaic for the moment the first event began.
5 heavy snow, 2 winter storm, 1 winter weather. Local standard time, as filed.
A trained spotter 6 miles northeast of Heron reported 7.5 inches of snow that fell in 12 hours.
A COOP observer 9 miles NNE of YAAK reported 11.8 inches of snow that fell in 24 hours.
The Montana DOT reported an estimated 6 to 8 inches of snow that fell between Haugan and Lookout Pass on Interstate 90. They reported not much wind at the pass and visibilities were reduced due to falling snow and fog. Chains were required on westbound towing units at the pass starting at 0615MST.
The Lincoln county 911 dispatcher reported an estimated 12 inches in Troy overnight.
A trained spotter one mile WNW of Elliston reported an estimated 10 inches of snow that fell in 11 hours. They also reported estimated wind gusts to 45 mph with visibilities reduced to one quarter mile due to blowing snow.
At 0735MST, Montana Highway Patrol reported that a jackknifed semi truck on Interstate 90 westbound at mile marker 90. Montana DOT reported snow-covered roads at this time in Frenchtown.
A COOP observer located at 10 miles SW of Happy's Inn reported 7.8 inches of snow.
Montana DOT reported severe driving conditions along Highway 2 from Java to Marias Pass from 1700MST on December 17 through the overnight. They also reported an estimated 8 inches of snow at Marias Pass, white-out conditions due to blowing snow and slick roads. At 0736MST on December 18, near whiteout conditions from blowing snow with estimated winds over 40 mph were reported by the MT DOT at Marias Pass.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2012Every state in 2012This day in weather historyWarnings in Montana, December 2012
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: 426473, 424646, 424654, 424858, 426475, 424860, 424652, 426478.