An upper level trough brought moderate to heavy snow to north-central Idaho. Over a foot and a half of snow fell at Lost Trail Pass while other locations saw less accumulations.
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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 upper level trough brought moderate to heavy snow to north-central Idaho. Over a foot and a half of snow fell at Lost Trail Pass while other locations saw less accumulations.
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 12, 2:20 PM PST, 5 hours 40 minutes earlier.
Area Forecast Discussion
National Weather Service Missoula MT
320 PM MST SAT DEC 12 2015
...Hazardous Winter Travel Conditions Tonight through Monday...
...Unsettled Weather with Much Colder Temperatures Next Week...
.DISCUSSION...
The next weather system is right on our doorstep as of this
afternoon, and will begin to move through Idaho and western
Montana by this evening. This storm will bring several rounds of
winter weather; one this evening and tonight affecting areas
generally west of Missoula, and another later Sunday into Monday,
impacting areas generally south of I-90. The first round will have
the biggest travel impacts along I-90 over Lookout Pass to Haugan
and Highway 12 over Lolo Pass, where over a foot of snow is
expected. Wet westerly flow will favor all west-facing slopes from
the Bitterroot Crest westward, with gusty winds in addition to the
snow.
As the trough deepens Sunday, the area of heaviest precipiationwill
shift into a southwest-to-northeast oriented band from the central
mountains of Idaho through southwest Montana, and slowly progress
eastward through Monday. Areas such as Highway 93 over Lookout
Pass and I-90 from Butte over Homestake Pass and east of the
Continental Divide will likely see well over a foot by the time
the storm exits the area. In addition, a cold front will push
across Lemhi County Idaho and southwest Montana Sunday night,
resulting in reduced visibilities with blowing snow. Elsewhere,
northwest Montana and populated valleys from Kalispell to Missoula
may see snow mix with rain at times Sunday, but will likely see
travel impacts as well, especially towards the Monday morning
commute for the Bitterroot Valley. Northwest Montana will be
spared the heaviest snow Sunday night. Lastly, the Camas Prairie
region of Idaho may see upslope snow increase in intensity by
Monday as snow levels lower, impacting Grangeville to Whitebird
Summit.
Bottom line: expect difficult travel at times this weekend,
especially in the higher terrain and over mountain passes, due to
both snow and wind.
Light snow will linger over the Northern Rockies Monday night
through Tuesday morning as the wrap around moisture from the
exiting low pressure interacts with a northerly upslope flow.
Most of the accumulating snowfall will be in the Butte/Blackfoot
region, with an additional 2-3 inches of snow. Locations west and
south of I-90, including central Idaho, will only see light
accumulations, around a trace to 1 inch of snow. Most of the area
will see a break in the snow Tuesday afternoon and evening as the
upper-level flow transitions to a northwesterly flow. A shortwave
trough will move through the flow, allowing light widespread snow
to once again impact the region in a 24 hour period starting
Wednesday morning. Typically in this scenario snowfall remains
fairly light. Though, 1 to 3 inches of snow will be possible for
the valleys of western Montana and central Idaho. The mountain
passes could see accumulations up to 5 inches. Snow levels will be
low enough for all valleys in the locations mentioned above, to
see at least a trace of snow.
Temperatures will remain fairly cold, and below normal for the
rest of the week, with no new snow impacting the region. Patchy
fog will however impact some valley locations of western Montana
and central Idaho, creating slick roads due to below-freezing
temperatures. The short break in the active weather could come to
an end by the start of next weekend, with another potentially
strong winter storm entering the region. Stay tuned!
&&
.AVIATION...
Light snow showers will continue off and on for KMSO and KGPI,
which could temporarily reduce visibility and obstruct mountains
from brief low ceilings. A strong winter system approaches this
evening, bringing moderate to heavy snow and low
visibility/ceilings to western Montana and north-central Idaho.
KGPI, KMSO, and KSMN will start to see impact around 13/0600Z and
continue through Sunday. Snow impacts at KBTM will begin generally
after 13/1200Z. Moderate to strong westerly winds aloft will
increase tonight through Sunday morning, with 40-50 kts right
above mountain ridges. Southerly winds of 10-15 kts are possible
near the surface for all terminals overnight into Sunday morning,
as well. Cold frontal passage from the northwest is expected to
pass through northwest Montana and KGPI between 13/1500Z and
13/1800Z, and reach KMSO between 13/2100Z and 14/0000Z.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Warning from 8 AM Sunday to 11 PM MST Monday
Butte/Blackfoot Region...Potomac/Seeley Lake Region.
Winter Storm Warning until 11 AM MST Monday Bitterroot/Sapphire
Mountains...Lower Clark Fork Region.
Winter Weather Advisory until 11 AM MST Monday
Missoula/Bitterroot Valleys.
Winter Weather Advisory until 11 AM MST Monday Flathead/Mission
Valleys...Kootenai/Cabinet Region.
Winter Weather Advisory until 11 AM MST Monday West Glacier
Region.
ID...Winter Storm Warning from 8 AM Sunday to 11 PM MST Monday
Eastern Lemhi County.
Winter Storm Warning until 11 AM MST /10 AM PST/ Monday Lower
Hells Canyon/Salmon River Region...Northern Clearwater
Mountains...Southern Clearwater Mountains...Western Lemhi
County.
&&The national radar mosaic for the moment the first event began.
3 winter weather, 2 winter storm. Local standard time, as filed.
Two inches of snow fell at Pierce while higher elevations saw 5 to 9 inches. Web cams during the event showed snow on roadways (i.e. Grangemont on Highway 11).
Higher elevations SNOTEL sensors reported anywhere from 6 to 12 inches of snowfall with this event. The SNOTEL at Lolo Pass only reported 5 inches. The Elk City web cam revealed snow covered roads by 5 am on the 13th.
Williams Creek received 12 to 16 inches of snowfall during this period. Blowing snow was also reported.
Lost Trail Pass received 21 inches of snow with periods of blowing snow during this event. Wind gusts to 25 mph were reported at 10 pm MST on the 12th which contributed to lower visibility from the falling and blowing snow. Snow plows had a hard time keeping up at times at Lost Trail Pass. Seven and a half inches of snow fell in the Salmon area while 4 to 6 inches fell in the Leadore area. Gilmore Summit saw strong gusty winds to 42 mph at times with blowing snow and slick conditions.
The web cam and weather sensor at White Bird Hill revealed light to moderate snow that brought slick conditions.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Idaho in 2015Every state in 2015This day in weather historyWarnings in Idaho, December 2015
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: 612852, 612853, 612863, 612864, 612860.