After being in cold Arctic air, overrunning warm and moist air caused moderate to heavy snow and produced poor visibilities and very slick roads.
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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.
After being in cold Arctic air, overrunning warm and moist air caused moderate to heavy snow and produced poor visibilities and very slick roads.
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 14, 3:12 PM MST, 2 hours 48 minutes earlier.
Area Forecast Discussion
National Weather Service Missoula MT
312 PM MST Wed Dec 14 2016
.DISCUSSION...A stratus layer and high clouds have kept many
locations in western Montana and north-central Idaho from warming
to their potential highs this afternoon. This will help set up the
upcoming winter system tonight. Also, a low stratus deck over
Lookout Pass has been sitting in what we call the dendritic zone
(snow growth zone), because of that, just enough moisture in the
air has created snow only over the pass. This will continue over
the next couple hours, so expect scattered snow and ice as you
reach the pass.
Snow is still on track to move into the region this evening with
main accumulations to be overnight through Thursday morning. The
lack of warming today makes for a really good temperature profile
for snow with the approaching warm front, so we have fairly high
confidence for snow to fall in most places by Thursday morning.
There is a line from Grangeville through Hamilton to Butte where
all the pieces may line up for longer periods of moderate to heavy
snow and thus respectable snow amounts of 5 or more inches of
snow by mid-morning. Those with the most favorable snow production
will see periods of higher snow rates that could add overtime for
snow accumulations. Those that are not in the main focus area
will generally have 3 inches or less. Temperatures are forecast to
warm some during Thursday afternoon and snow accumulations will
taper off.
The arctic is still on track to move into western Montana
Thursday evening and especially overnight. The wind with the
expected cold air may blow snow around and there is the potential
for additional snow with the frontal passage especially in
southwest Montana through Lemhi County Idaho. Cold wind chills of
negative 10 to negative 20 are also likely with the wind Friday
and Friday night.
Another focus area for Thursday night snow is Orofino, the Camas
Prairie, Grangeville, and much of north central Idaho through
Friday morning, so this will likely be another impact period with
cold temperatures and another very favorable snow setup.
With the Arctic airmass in place combined with clearing skies, a
very frigid night is expected across the northern Rockies Friday
night. Temperatures below zero is expected across all of western
Montana with some valleys along the Continental Divide and
northwest Montana may see temperatures of 20 below zero.
A northwesterly flow will setup across the Northern Rockies Monday
behind the retreating arctic, that will keep snow showers in the
forecast for western region. Starting Tuesday, a series of
shortwaves will slide through the northwesterly flow enhancing
the possibility for more significant mountain and mountain pass
snowfall through the rest of the week. The valleys will likely be
shadowed out for the most part, however, we can't rule out periods
of light snow accumulations for western Montana valleys at times
during the week. Keep up on the forecast as we go through the
weekend and get closer to these impact periods.
&&
.AVIATION...A low stratus deck and mid-level clouds have and will
continue to obscure mountain ranges throughout the Northern
Rockies this afternoon and evening. A warm front will be moving
north overnight tonight that will bring widespread light to
moderate snow to the region. Low visibility and ceilings due to
snow will be likely for KSMN starting around 15/0400Z, and
15/0900Z for KMSO and KBTM. Several inches of snow will be
possible for these aviation sites by tomorrow afternoon/evening.
KGPI will see light snow, but not to the degree as areas south of
the I-90 Corridor. Snow intensities will tapper off for most areas
by 16/00Z.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory until 11 AM MST Thursday
Bitterroot/Sapphire Mountains.
Winter Weather Advisory until 11 AM MST Thursday Potomac/Seeley
Lake Region.
Winter Weather Advisory until 11 AM MST Friday Butte/Blackfoot
Region.
Winter Weather Advisory until 11 AM MST Thursday Lower Clark
Fork Region.
Winter Weather Advisory until 11 AM MST Thursday
Missoula/Bitterroot Valleys.
ID...Winter Weather Advisory until 10 AM PST Thursday Northern
Clearwater Mountains...Southern Clearwater Mountains.
Winter Weather Advisory until 11 AM MST Thursday Eastern Lemhi
County...Western Lemhi County.
Winter Weather Advisory until 10 AM PST Thursday Lower Hells
Canyon/Salmon River Region...Orofino/Grangeville Region.
&&The national radar mosaic for the moment the first event began.
6 heavy snow. Local standard time, as filed.
Moderate to heavy snow caused slick roads and low visibility during this event. Total snow amounts include 13 at Lost Trail, 10.5 five miles east of Sula, 9.5 fourteen miles northeast of Sula, and near 6 west of Lolo.
A combination of moderate to heavy snow, snow-covered roads, and low visibility created high impact to travel. The poor visibilities were caused by vehicles stirring up the very light snow on the surface. Chains were required for US-93 to Evaro Hill during the morning commute on the 15th. Total snow amounts: 5.3 at Alberton, 4 at Haugan and Evaro Hill, and 3 at Thompson Falls.
A combination of moderate to heavy snow, snow-covered roads, and low visibility created high impact to travel. The poor visibilities were caused by vehicles stirring up the very light snow on the surface. The snow fell heavy enough that there was barely one lane on Interstate 90 at times. Snow amounts: 9 Deer Lodge, 7 Georgetown Lake, 6 Elliston, and 3 Anaconda and Ovando.
A combination of moderate to heavy snow, snow-covered roads, and low visibility created high impact to travel. The poor visibilities were caused by vehicles stirring up the very light snow on the surface. Multiple vehicle slide-offs were reported, and there was a snow plow that slid off the road near Bonner. Total snow amounts: 10 Lindbergh Lake, 6.4 Seeley Lake, 6 Bonner and Clinton, and 4 Greenough Hill.
Between 8 and 14 inches of heavy snow fell from the Polson area east to Highway 35 on the east side of Flathead Lake. Also a combination of moderate to heavy snow, snow-covered roads, and low visibility created high impact to travel in the Mission Valley. The poor visibilities were caused by vehicles stirring up the very light snow on the surface. Other snow amounts include 4 NW of St. Ignatius, 2.4 at Glacier Park International Airport and 2.2 at Ronan.
A combination of moderate to heavy snow, snow-covered roads, and low visibility created high impact to travel. The poor visibilities were caused by vehicles stirring up the very light snow on the surface. Total snow amounts include 13 at Darby and 2 miles WNW of Stevensville, 8 at Hamilton, 7.5 3 miles east of Florence, 7 in the South Hills of Missoula, and 6.3 at the Missoula International Airport.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2016Every state in 2016This day in weather historyWarnings in Montana, December 2016
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: 667565, 667553, 667555, 667554, 667556, 667550.