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.

Dense Fog in SOUTHERN ROCKY MOUNTAIN FRONT, MONTANA
From 21-DEC-20 15:55:00 to 21-DEC-20 22:55:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Choteau airport shows period of dense fog with visibilities under 1/2mi at times.

Dense Fog in EASTERN GLACIER, MONTANA
From 21-DEC-20 16:33:00 to 22-DEC-20 00:45:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Cut Bank Airport repots dense fog with visibilities under 1/2mi at times.

Dense Fog in CASCADE, MONTANA
From 21-DEC-20 17:41:00 to 21-DEC-20 21:24:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Great Falls airport reports visibility 1/2 mi or less in fog.

Dense Fog in HILL, MONTANA
From 21-DEC-20 22:56:00 to 22-DEC-20 06:58:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Havre airport reports dense fog with visibilities of 1/2 mi or less at times.

High Wind in BROADWATER, MONTANA
From 22-DEC-20 10:03:00 to 22-DEC-20 10:03:00 (MST-7)
Magnitude: 50.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Mesonet station ginm8 ginger raws.

Heavy Snow in BEAVERHEAD, MONTANA
From 21-DEC-20 10:00:00 to 22-DEC-20 12:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Estimated about a foot of wind-blown snow during the afternoon and evening of dec 22nd.

High Wind in FERGUS, MONTANA
From 22-DEC-20 14:56:00 to 22-DEC-20 14:56:00 (MST-7)
Magnitude: 56.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Awos station k1om oscar. vis 3sm -sn.

High Wind in FERGUS, MONTANA
From 22-DEC-20 15:15:00 to 22-DEC-20 15:15:00 (MST-7)
Magnitude: 53.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Awos station kmvh n bar ranch awos.

High Wind in GALLATIN, MONTANA
From 20-DEC-20 15:00:00 to 20-DEC-20 15:00:00 (MST-7)
Magnitude: 61.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Mesonet station gnfhy 10.7 w emigrant (avalanche).

High Wind in GALLATIN, MONTANA
From 22-DEC-20 07:04:00 to 22-DEC-20 07:04:00 (MST-7)
Magnitude: 55.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Mesonet station ylwm8 yellow mule raws.

High Wind in MADISON, MONTANA
From 22-DEC-20 11:00:00 to 22-DEC-20 11:00:00 (MST-7)
Magnitude: 51.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Mesonet station ycams 5.7 w big sky (avalanche).