Winter Storm and High Wind in Montana, December 20, 2016

Name: Winter Storm and High Wind in Montana, December 20, 2016
Start: 2016-12-20T01:00
End: 2016-12-20T18:30
Location: Montana

December 20, 2016 · NWS MSO · 3 events in 3 counties and zones

A robust shortwave brought heavy mountain snow, mixed precipitation and strong gusty winds. Cold surface temperatures contributed to icy conditions in valley locations.

Where it happened

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.

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

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The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 3

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.

What happened

The episode as NWS MSO wrote it up.

A robust shortwave brought heavy mountain snow, mixed precipitation and strong gusty winds. Cold surface temperatures contributed to icy conditions in valley locations.

What forecasters said that day

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, 9:40 PM MST, 3 hours 20 minutes earlier.

Area forecast discussion, Dec 19, 9:40 PM MST, 3 hours 20 minutes before

Area Forecast Discussion
National Weather Service Missoula MT
940 PM MST Mon Dec 19 2016

.UPDATE...Only updated this discussion to remove the expired
Advisories and Warnings.

&&

.DISCUSSION...Outside of canceling Winter Weather Advisories and
Warnings in effect earlier today, no further updates were needed
to tonight's forecast.

&&

.AVIATION...Snow showers are currently on the decrease with only a
few light snow showers possible at area terminals. A much stronger
weather system is expected to start moving in after midnight
tonight and will bring widespread impacts to area terminals on
Tuesday. For Tuesday, a mixture of rain/snow/freezing rain will
be possible for area terminals. By Tuesday afternoon, a vigorous
cold front will push through and will bring strong gusty winds and
snow showers. Some of the snow showers could be intense in the
afternoon. Widespread mountain obscurations with lowered ceilings
and low visibility is expected with the snow showers on Tuesday.

&&

.PREV DISCUSSION... /ISSUED 246 PM MST Mon Dec 19 2016/

DISCUSSION...The first in a series of wintry weather systems will
quickly shift to the east of the northern Rockies this evening
with improving conditions.

The next more vigorous weather system is due late tonight and
Tuesday. This weather system will deliver moderate to heavy snow
to the high terrain and a mix of snow, patchy freezing rain, and
rain to the valleys of west central Idaho and western Montana. The
Camas Prairie to Orofino areas will be impacted first after
midnight with periods of snow and local freezing rain. High winds
are expected to develop in the Camas Prairie early Tuesday causing
additional blowing and drifting snow. Strong winds should also
develop in the mountains and some valleys of western Montana
(especially the Bitterroot Valley and Anaconda to Deer Lodge)
Tuesday. The winds will further moderate the temperatures Tuesday
morning. However, the very cold ground will probably support
intermittent freezing rain, especially the Bitterroot Valley
northward across Missoula and to about Plains and the Mission
Valley early Tuesday.

For Tuesday and Tuesday evening, 12 to 20 inches of snow is
expected in the Clearwaters and Bitterroots Mountains. If that was
not enough...the atmosphere may become very favorable for the
development of intense snow bands from the Clearwaters eastward
across the Bitterroots late Tuesday. However, the exact locations
and intensity of the snow bands are still to be determined. A cold
front will deliver a colder air mass back over the northern
Rockies Tuesday afternoon and evening.

Weak high pressure and a temporary break is expected Wednesday
into early Thursday.

Another weather system is expected late Thursday into Friday and
will mostly impact the mountains. However, some light scattered
valley precipitation is expected.

A more impressive wintry weather system may develop Friday night
into the weekend. Latest model guidance shows a low pressure
system developing over the Great Basin and slowly shifting
northward over the the Northern Rockies. This scenario may also
again draw colder air from Canada southward over the region. There
is still a fair amount of uncertainty on where most of the light
to moderate snow may fall...but at this time southwest Montana,
west central Montana and Lemhi County have the highest probability
of seeing more snow.

AVIATION...Snow showers are currently on the decrease with only a
few light snow showers possible at area terminals. A much stronger
weather system is expected to start moving in after midnight
tonight and will bring widespread impacts to area terminals on
Tuesday. For Tuesday, a mixture of rain/snow/freezing rain will
be possible for area terminals. By Tuesday afternoon, a vigorous
cold front will push through and will bring strong gusty winds and
snow showers. Some of the snow showers could be intense in the
afternoon. Widespread mountain obscurations with lowered ceilings
and low visibility is expected with the snow showers on Tuesday.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Warning until 11 PM MST Tuesday Lower Clark Fork
     Region.

     Winter Weather Advisory from 3 AM to 6 PM MST Tuesday
     Flathead/Mission Valleys...Kootenai/Cabinet Region.

     Winter Weather Advisory from 3 AM Tuesday to midnight MST
     Tuesday night Potomac/Seeley Lake Region...West Glacier
     Region.

     Winter Storm Warning from 2 AM to 11 PM MST Tuesday
     Bitterroot/Sapphire Mountains.

     Winter Weather Advisory from 3 AM to 10 AM MST Tuesday
     Missoula/Bitterroot Valleys.

ID...High Wind Warning from 1 AM to 10 AM PST Tuesday
     Orofino/Grangeville Region.

     Winter Storm Warning until 10 PM PST Tuesday Northern Clearwater
     Mountains...Southern Clearwater Mountains.

     Winter Weather Advisory from 3 AM to noon MST Tuesday Eastern
     Lemhi County...Western Lemhi County.

&&

The radar

The national radar mosaic for the moment the first event began.

Open the radar archive at this moment

Event by event

2 winter storm, 1 high wind. Local standard time, as filed.

Winter Storm, Lower Clark Fork Region

When: December 20, 1:00 AM MST to 3:00 PM MST
Where: Lower Clark Fork Region forecast zone
Reported by: Department of Highways
Coordinates: 47.286, -114.685 (the zone’s center; the record gives no point)

Lookout Pass received 12 to 14 inches of snow with strong gusty winds near 40 mph during the event. Freezing rain was reported in sections of Sanders County causing road conditions to be treacherous at times. Portions of Mineral County also saw several hours of freezing rain.

Winter Storm, Bitterroot / Sapphire Mountains

When: December 20, 3:00 AM MST to 3:00 PM MST
Where: Bitterroot / Sapphire Mountains forecast zone
Reported by: Park/Forest Service
Coordinates: 46.508, -113.828 (the zone’s center; the record gives no point)

Lolo Pass received 13 inches of snow during the event, and there were reports of whiteout conditions with blowing and drifting snow. A worker at the pass reported that it was the worst conditions he had seen in 13 years. The winds were so strong that a tree had blown into the west bound lane north of the pass.

High Wind, Butte / Blackfoot Region

When: December 20, 4:30 PM MST to 6:30 PM MST
Where: Butte / Blackfoot Region forecast zone
Measured: 54 kt (62 mph) measured gust
Reported by: Mesonet
Coordinates: 46.306, -113.025 (the zone’s center; the record gives no point)

Sustained winds of 45 mph with a gust to 62 was measured by the MDT sensor located north of Avon. A trained spotter located two miles north of Deer Lodge reported wind gusts over 60 mph. Also there was a short period of blizzard conditions around 5 pm at MacDonald Pass when the cold front went through.

What these are

Winter Storm: A storm that brought snow, sleet or freezing rain at warning levels, usually over several hours or days.
High Wind: Sustained non-thunderstorm winds of 40 mph or more for an hour, or gusts of 58 mph or more.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in Montana in 2016 Every state in 2016 This day in weather history Warnings in Montana, December 2016

Sources

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: 668673, 668674, 668675.