A Canadian cold front advanced southward into North-Central Montana on Monday, December 18th. Marked frontogenesis triggered bands of steady to heavy snow along and near the Hi-Line. As the front advanced farther southward, the frontogenesis and associated snow banding weakened over Central Montana in response to an already cool air mass over Southwest Montana, ahead of the front. Simultaneously, steady to heavy upslope snow fell along the Rocky Mountain Front due to moist westerly flow aloft.  Then, as a shortwave trough advanced from the Pacific Northwest to the Great Basin, associated lift, including isentropic lift, generated widespread light to moderate snow over North-Central and Southwest Montana on December 19th into the 20th.

Winter Storm in HILL, MONTANA
From 20-DEC-17 12:05:00 to 20-DEC-17 12:05:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

MT Highway Patrol reported a vehicular crash along 2nd Street West in Havre. No injuries. Observations from nearby Havre Airport ASOS indicate it was likely snowing lightly with 1.5 mile visibility at time of crash.

Winter Storm in SOUTHERN ROCKY MOUNTAIN FRONT, MONTANA
From 19-DEC-17 11:19:00 to 19-DEC-17 11:19:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Fresh snowfall of 14 inches during the overnight into late morning hours. Location: 19-miles WNW of Choteau.

Winter Storm in FERGUS, MONTANA
From 20-DEC-17 14:05:00 to 20-DEC-17 14:05:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

MT DOT reported closure of US-191 from Eddie's Corner to Harlowton.

Winter Storm in JUDITH BASIN, MONTANA
From 20-DEC-17 14:05:00 to 20-DEC-17 14:05:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

MT DOT reported closure of US-191 from Eddie's Corner to Harlowton.

Winter Storm in CASCADE, MONTANA
From 19-DEC-17 11:05:00 to 19-DEC-17 11:05:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

MT DOT reported severe driving conditions from accumulating snow along US-87 from Great Falls to Fort Benton.

Winter Storm in CHOUTEAU, MONTANA
From 19-DEC-17 11:05:00 to 19-DEC-17 11:05:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

MT DOT reported severe driving conditions from accumulating snow along US-87 from Great Falls to Fort Benton.

Winter Storm in SOUTHERN LEWIS AND CLARK, MONTANA
From 20-DEC-17 08:50:00 to 20-DEC-17 08:50:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

MT DOT webcam indicated poor visibility and falling snow resulted in hazardous driving conditions along MacDonald Pass (US-12).

Winter Storm in MEAGHER, MONTANA
From 20-DEC-17 12:41:00 to 20-DEC-17 12:41:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

MT Highway Patrol reported a vehicular crash during snowstorm. Occurred along US-89 near mile marker 14.

Winter Storm in NORTH ROCKY MOUNTAIN FRONT, MONTANA
From 19-DEC-17 16:45:00 to 19-DEC-17 16:45:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

MT DOT reported single vehicle accident along MT Route 464 near Saint Mary. Roadway was snow and ice-covered.

Heavy Snow in JEFFERSON, MONTANA
From 20-DEC-17 17:19:00 to 20-DEC-17 17:19:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Spotter reported 9.5 inches of fresh snow since 0800 MST on Dec 20th.