High Wind, Gallatin
- When
- December 20, 3:00 PM MST
- Where
- Gallatin forecast zone
- Measured
- 61 kt (70 mph) measured gust
- Reported by
- Mesonet
Mesonet station gnfhy 10.7 w emigrant (avalanche).
Heavy Snow and High Wind in Montana, December 20 to 22, 2020
Behind a warm front that pushed through the area on the the 21st, weak easterly flow along with clearing skies resulted in a widespread dense fog developing across the plains of North-Central Montana. This dense fog was mainly an issue during the overnight hours, as strong winds moving in would result in the mixing out of this fog bank.
The toll
- Deaths
- 0
- Injuries
- 0
- Property damage
- None recorded
- Crop damage
- None recorded
- Events
- 11
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 TFX wrote it up.
Behind a warm front that pushed through the area on the the 21st, weak easterly flow along with clearing skies resulted in a widespread dense fog developing across the plains of North-Central Montana. This dense fog was mainly an issue during the overnight hours, as strong winds moving in would result in the mixing out of this fog bank.
During the day on Tuesday (the 22nd), a well defined shortwave trough moved through the area, with an attendant surface low pressure system that emerged east of the Rockies in SW Alberta, deepening as it did so. This system would bring a Pacific cold front through the area early in the morning. Behind the cold front, winds would increase and support gusts to 35-45 mph across most of the plains. There was a risk of stronger winds further to the east, and a High Wind Warning was issued for Blaine, Fergus, and Judith Basin counties due to this threat.
Event by event
6 high wind, 4 dense fog, 1 heavy snow. Local standard time, as filed.
Heavy Snow, Beaverhead
- When
- December 21, 10:00 AM MST to December 22, 12:00 PM MST
- Where
- Beaverhead forecast zone
- Reported by
- Trained Spotter
Estimated about a foot of wind-blown snow during the afternoon and evening of dec 22nd.
Dense Fog, Southern Rocky Mountain Front
- When
- December 21, 3:55 PM MST to 10:55 PM MST
- Where
- Southern Rocky Mountain Front forecast zone
- Reported by
- AWOS
Choteau airport shows period of dense fog with visibilities under 1/2mi at times.
Dense Fog, Eastern Glacier
- When
- December 21, 4:33 PM MST to December 22, 12:45 AM MST
- Where
- Eastern Glacier forecast zone
- Reported by
- ASOS
Cut Bank Airport repots dense fog with visibilities under 1/2mi at times.
Dense Fog, Cascade
- When
- December 21, 5:41 PM MST to 9:24 PM MST
- Where
- Cascade forecast zone
- Reported by
- ASOS
Great Falls airport reports visibility 1/2 mi or less in fog.
Dense Fog, Hill
- When
- December 21, 10:56 PM MST to December 22, 6:58 AM MST
- Where
- Hill forecast zone
- Reported by
- ASOS
Havre airport reports dense fog with visibilities of 1/2 mi or less at times.
High Wind, Gallatin
- When
- December 22, 7:04 AM MST
- Where
- Gallatin forecast zone
- Measured
- 55 kt (63 mph) measured gust
- Reported by
- Mesonet
Mesonet station ylwm8 yellow mule raws.
High Wind, Broadwater
- When
- December 22, 10:03 AM MST
- Where
- Broadwater forecast zone
- Measured
- 50 kt (58 mph) measured gust
- Reported by
- Mesonet
Mesonet station ginm8 ginger raws.
High Wind, Madison
- When
- December 22, 11:00 AM MST
- Where
- Madison forecast zone
- Measured
- 51 kt (59 mph) measured gust
- Reported by
- Mesonet
Mesonet station ycams 5.7 w big sky (avalanche).
High Wind, Fergus
- When
- December 22, 2:56 PM MST
- Where
- Fergus forecast zone
- Measured
- 56 kt (64 mph) measured gust
- Reported by
- AWOS
Awos station k1om oscar. vis 3sm -sn.
High Wind, Fergus
- When
- December 22, 3:15 PM MST
- Where
- Fergus forecast zone
- Measured
- 53 kt (61 mph) measured gust
- Reported by
- AWOS
Awos station kmvh n bar ranch awos.
What these are
- High Wind
- Sustained non-thunderstorm winds of 40 mph or more for an hour, or gusts of 58 mph or more.
- Heavy Snow
- Snowfall reaching the local warning threshold without the other hazards of a winter storm.
- Dense Fog
- Fog reducing visibility to a quarter mile or less, filed where it caused accidents or disruption.
After NWS Directive 10-1605, the rules offices file Storm Data by.
The same day elsewhere
- High Surf in American Samoa, December 20, 2020
- Dense Fog in California, December 20 to 21, 2020
- Heavy Snow and High Wind in Washington, December 20 to 22, 2020
- Dense Fog in California, December 20 to 21, 2020
- High Wind in Colorado, December 20 to 21, 2020
- High Wind in South Dakota, December 20, 2020
- Freezing Fog in Idaho, December 20, 2020
- Marine Thunderstorm Winds in South Atlantic Coastal Waters, December 20, 2020
- High Wind in Wyoming, December 20, 2020
- Marine Thunderstorm Wind in Gulf of Mexico, December 20, 2020
More
Every storm in Montana in 2020Every state in 2020This day in weather historyWarnings in Montana, December 2020
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 2026-10-01. Each event’s entry at NCEI: 928364, 928354, 928348, 928349, 928351, 928352, 928368, 928353, 928371, 928357, 928362.