A moist overrunning snow event that brought up to 10 inches across northwest Montana. There were multiple car slide-offs and accidents that were reported during this event.
Every event with a place to put it; 3 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 moist overrunning snow event that brought up to 10 inches across northwest Montana. There were multiple car slide-offs and accidents that were reported during this event. During the storm, a person in an automobile was killed (indirect) when their vehicle lost control in the snow and hit another vehicle head-on.
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 19, 2:43 PM MST, 3 hours 17 minutes earlier.
Area Forecast Discussion
National Weather Service Missoula MT
243 PM MST Wed Dec 19 2012
...Significant snow over Clearwater county and Northwest Montana...
.DISCUSSION...A southerly pressure gradient has developed over
southwestern Idaho county and will linger through Thursday
morning. This pressure gradient will cause wind gusts up to 35 mph
across the highway 95 corridor from Riggins to Whitebird grade and
over the Camas prairie. The winds will decrease on Thursday as the
pressure gradient relaxes.
A plume of moisture will move into Clearwater county and up into
northwest Montana. This moisture will cause fairly steady snow
across the aforementioned area tonight through Thursday. Places like
Lookout pass, Bull Lake road, Troy/Yaak/Libby/Eureka region and
Glacier park area could see 5 to 10 inches of new snow over the next
24 hours. The other areas under advisories could see up to 5
inches, while the Flathead valley could see around 2 inches
during the morning commute. This snow will cause hazardous driving
conditions. Marias pass has the added impact of gusty westerly
winds during this event causing blowing snow at times. The winds
associated with this feature will not be as strong as the event on
Monday night into Tuesday.
The Northern Rockies will remain under a southwesterly flow pattern
through the remainder of the week. The bulk of the moisture will
move out of the area, but the higher terrain across northwest
Montana could see off/on snow showers. Also this southwesterly flow
will bring in a warmer airmass allowing temperatures to be above
normal by Friday.
The models are showing that the southwesterly flow will persist
through the Saturday time frame before the trough comes on shore.
The models have come in line with the trough to become more of a
westerly flow pattern with pulses of moisture to move through the
area on Sunday through Monday night. The best energy and moisture
are expected to slide south of the Northern Rockies, but the region
should see widespread precipitation from this pattern. The models
are still showing an arctic airmass sliding down Sunday into
Monday, but how much cold air filters into western Montana is
still uncertain. A ridge of high pressure will build over the area
by mid next week, but the models diverge on the strength and
timing of this ridge.
&&
.AVIATION...Cloud cover is increasing throughout the region
associated with the next weather system. Snow is also increasing
in coverage through eastern Washington and this snow will move
into north central Idaho and northwest Montana by this evening.
Model guidance show the main impacted areas to be from northwest
Montana and westward under southwesterly flow aloft. Low
visibilities and ceilings due to snow will be common at KGPI and
surrounding areas including the terrain from the ID/MT border
through the divide tonight through Thursday. Terrain winds from the
southwest and west are also forecast to increase which will create
additional impacts to the high terrain and Mountain passes.
Elsewhere, cloud cover will lower but snow will be much lighter,
so the other TAF sites should not have the impacts that KGPI will
have through Thursday.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY until 11 AM MST Thursday Lower Clark
Fork Region.
WINTER WEATHER ADVISORY from 11 PM this evening to 11 AM MST
Thursday Flathead/Mission Valleys.
WINTER WEATHER ADVISORY from 11 PM this evening to 5 PM MST
Thursday West Glacier Region.
WINTER WEATHER ADVISORY until 11 AM MST Thursday
Kootenai/Cabinet Region.
ID...WINTER WEATHER ADVISORY until 10 AM PST Thursday ABOVE 3000 FEET
FOR THE Northern Clearwater Mountains.
&&
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https://www.twitter.com/NWSMissoulaThe national radar mosaic for the moment the first event began.
2 heavy snow, 1 winter weather. Local standard time, as filed.
A trained spotter 12 miles northwest of Troy at 2410 feet MSL reported a snow storm total of 8.0 inches with a snow depth of 18 inches.
A trained spotter 4 miles northwest of Troy estimated a snow storm total of 10.0 inches.
A member of the public located 2 miles ENE of Libby reported an estimated 7 inches of snow. A 67-year-old woman from Libby died as a result of injuries from a head-on accident that occurred at 1442MST on December 20th at milepost 22.1 on Highway 2 west of Libby. The report says that her vehicle lost control in the snow and slush on the roads.
As the offices recorded each death: direct deaths were caused by the weather itself, indirect ones by something it set in motion.
| Event | Date | Age | Sex | Where | Kind |
|---|---|---|---|---|---|
| Winter Weather, Kootenai/Cabinet Region | 2012-12-20 | 67 | Female | Vehicle/Towed Trailer | Indirect |
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: 426435, 426437, 424865.