Strong Wind in Montana, December 1, 2021

Name: Strong Wind in Montana, December 1, 2021
Start: 2021-12-01T00:00
End: 2021-12-01T15:00
Location: Montana

December 1, 2021 · NWS MSO · 2 events in 2 counties and zones

Strong westerly winds led to power outages across portions of Northwest Montana on December 1st. A Pacific jet was present across the Pacific Northwest and Northern Rockies.

Where it happened

Every event with a place to put it; 2 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.

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The toll

Deaths: 0
Injuries: 0
Property damage: $3,000
Crop damage: None recorded
Events: 2

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.

Strong westerly winds led to power outages across portions of Northwest Montana on December 1st. A Pacific jet was present across the Pacific Northwest and Northern Rockies. Unstable conditions allowed for gusty winds to mix down to the surface.

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 Nov 30, 5:32 PM MST, 6 hours 28 minutes earlier.

Area forecast discussion, Nov 30, 5:32 PM MST, 6 hours 28 minutes before

Area Forecast Discussion...corrected
National Weather Service Missoula MT
532 PM MST Tue Nov 30 2021

.UPDATE...Recent model trends point towards a strengthening
pressure gradient across western Montana Wednesday morning and
afternoon. Therefore, forecast winds on Wednesday have been
increased, particularly across mountain ranges in western Montana
and along the Continental Divide. Thick cloud cover and a stable
atmospheric profile will limit valley wind gust potential,
particularly for narrow-mountain valley locations. Broad valleys,
such as the Bitterroot and Flathead valley, and I-90 corridor from
Deer Lodge to Butte will be prone to stronger wind gusts up to 35
mph. Mountain locations will see wind gusts exceeding 45 mph,
with the strongest winds expected in the Anaconda-Pintler and
Bitterroot Mountains, and in Glacier National Park. The pressure
gradient will weaken on Thursday. The combination of cloud cover
and stable conditions will reduce the threat of wind gusts
exceeding 25 mph across valley locations. Therefore, the forecast
has been updated to reduce valley winds. Gusty winds in excess of
30 mph will continue across mountain locations. The strongest
winds will once again develop along the Continental Divide.
/Lukinbeal

AVIATION...Lingering moisture will allow for considerable
mountain obscurations through Wednesday morning with some light
showers on the terrain. Once we get to sunset, valleys will be
mostly dry but with patchy fog early Wednesday. A strengthening
southwesterly gradient and periodic cloud cover should limit fog
potential in most valleys but patchy fog is still possible.
Another slug of moisture will be focused on Northwest Montana on
Wednesday with low clouds and rain on the terrain. Light rain is
possible for the valleys on Northwest Montana on Wednesday but
with limited aviation impact. Occasionally gusty winds will occur
this afternoon and again on Wednesday with the southwesterly
pressure gradient in place.

&&

.PREV DISCUSSION... /ISSUED 230 PM MST Tue Nov 30 2021/

DISCUSSION...A low amplitude ridge of high pressure will persist
over the Northern Rockies for the next several days. Warm tropical
moisture continues to stream through this flow pattern at times.
This moisture will keep light precipitation going this afternoon
and evening. The moisture should transition up into Canada by
tomorrow, but parts of northwest Montana appear to have some
lingering shower activity. The warm air will keep temperatures
well above normal for the remainder of the work week, but readings
on Wednesday should break daily records.

A strong upper level winds will be draped over the Northern
through Thursday. These winds will cause breezy conditions in
valleys with the higher terrain along the Continental Divide
potentially experiencing damaging wind gusts.

The models are still indicating that a weak disturbance moves into
the Northern Rockies by Sunday allowing the upper level flow to
become more northwesterly. This transition would allow for cooler
air to move into the region potentially bringing the snow levels
down to valley floors finally.

AVIATION...Lingering moisture will allow for considerable
mountain obscurations through Wednesday morning with some light
showers on the terrain. Once we get to sunset, valleys will be
mostly dry but with patchy fog early Wednesday. A strengthening
southwesterly gradient and periodic cloud cover should limit fog
potential in most valleys but patchy fog is still possible.
Another slug of moisture will be focused on Northwest Montana on
Wednesday with low clouds and rain on the terrain. Light rain is
possible for the valleys on Northwest Montana on Wednesday but
with limited aviation impact. Occasionally gusty winds will occur
this afternoon and again on Wednesday with the southwesterly
pressure gradient in place.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&

The radar

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

Open the radar archive at this moment

Event by event

2 strong wind. Local standard time, as filed.

Strong Wind, West Glacier Region

When: December 1, 12:00 AM MST to 1:00 AM MST
Where: West Glacier Region forecast zone
Measured: 42 kt (48 mph) measured gust
Property damage: $1,000
Reported by: Mesonet
Coordinates: 47.971, -114.069 (the zone’s center; the record gives no point)

Southwesterly wind gusts of 40 mph or higher were observed at Marias Pass from midnight to 600 am on December 1st. A peak gust of 59 mph was observed at midnight. The Montana Department of Transportation reported a large tree blocking the eastbound lane of US Highway 2 at milepost 176. Flathead Electric COOP reported 353 residents without power in the vicinity of Essex, with power being restored by 619 am.

Strong Wind, Kootenai/Cabinet Region

When: December 1, 6:37 AM MST to 3:00 PM MST
Where: Kootenai/Cabinet Region forecast zone
Measured: 42 kt (48 mph) estimated gust
Property damage: $2,000
Reported by: Mesonet
Coordinates: 48.171, -114.863 (the zone’s center; the record gives no point)

Wind gusts of 30 to 50 mph were observed in the Kootenai/Cabinet region during the morning and afternoon hours of December 1st. The Flathead Electric COOP reported two power outages associated with tree damage, totaling 298 residents.

What these are

Strong Wind: Non-thunderstorm winds below high wind criteria that nonetheless caused damage or casualties.

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

The same day elsewhere

Every storm in Montana in 2021 Every state in 2021 This day in weather history Warnings in Montana, December 2021

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: 996847, 996848.