An upper level wave dropped out of British Columbia, embedded in northwesterly flow and brought periods of heavy snow to western Montana. A plume of moisture with tropical origins interacted with this wave, to provide higher snowfall amounts as compared with other northwest waves. Driving conditions were reported to be difficult at times especially along Interstate 90 from the Idaho border to just east of Missoula. Snowfall amounts ranged from 4 to 8 inches in the Valleys and up to a foot in the mountains of western Montana.

Winter Weather in KOOTENAI/CABINET REGION, MONTANA
From 20-DEC-13 10:00:00 to 20-DEC-13 23:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

A person from the public in Eureka reported 5 of total snowfall with this event. A person from 5 miles north of Fortine measured 4.5 of total snowfall.

Heavy Snow in LOWER CLARK FORK REGION, MONTANA
From 20-DEC-13 10:41:00 to 20-DEC-13 23:53:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Heavy snow was reported by MT DOT for I-90, especially from Alberton to Frenchtown and snow plows could barely keep up. The MT DOT also reported that US-93 at Evaro Hill experienced heavy snow for several hours during the afternoon and evening of Dec. 20. A weather spotter located in Alberton reported that conditions were severe on I-90, especially in the passing lane at 8:30 MST on Dec. 20. Snowfall amounts: 8 Evaro Hill, 6.7 Huson, 6.3 Frenchtown, and 5 lower Evaro Hill.

Heavy Snow in MISSOULA / BITTERROOT VALLEYS, MONTANA
From 20-DEC-13 13:27:00 to 21-DEC-13 01:53:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Snowfall was not as heavy in terms of sensible weather during this event, but because the timing occurred during high volume traffic, it became a high impact event. Steady snowfall continued during rush hour traffic on a weekend preceding the holidays, and this caused more people on the roads traveling to holiday parties etc. At 6:31 pm MST, the Missoula Sheriff's office issued an emergency alert asking people to stay off the roads, so that snow plows could efficiently mitigate poor road conditions. Several accidents were reported in the City of Missoula and along US-93 south to Victor.  In the immediate Missoula Valley, snowfall amounts ranged from 4.7 at the Missoula International Airport to 6 on the South Hills of Missoula. In the Bitterroot Valley from Lolo to Stevensville, snowfall amounts ranged from 6 to 8.

Heavy Snow in FLATHEAD/MISSION VALLEYS, MONTANA
From 20-DEC-13 11:53:00 to 20-DEC-13 23:22:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Official NWS Observations

The Glacier Park International Airport reported 5.4 of snow with 0.21 of liquid equivalent. A weather spotter in Columbia Falls tweeted that the powdery snow had fallen over icy roads, which made for slick driving at 12:26 pm MST and at 4:07 pm MST. This spotter measured a total of 8 of snow at 11:30 pm MST and reported that secondary roads had deep snow. Someone from Kalispell tweeted at 2:50 pm MST that the roads in Kalispell were nasty and suggested that people stay home. At 10:30 pm, a weather spotter located 2 miles NNW of Kalispell reported 8.3 of snow. The MT road incidents reported 10 automobile crashes with no injuries, 3 crashes with injuries and 8 slide-offs in the Flathead and Mission Valleys on Dec. 20.

Winter Weather in BITTERROOT / SAPPHIRE MOUNTAINS, MONTANA
From 20-DEC-13 07:00:00 to 21-DEC-13 03:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: SNOTEL

The Lolo Pass SNOTEL measured 6 of snow with 0.50 of snow water equivalent with this storm. The COOP located at Lolo Hot Springs measured 2 of snow with 0.12 of precipitation.

Heavy Snow in POTOMAC / SEELEY LAKE REGION, MONTANA
From 20-DEC-13 14:00:00 to 21-DEC-13 03:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Two different accidents involving multiple vehicles occurred on I-90 near Turah and also east of Clinton. The accident near Turah closed both lanes near 6:15 pm MST on Dec. 20. Road conditions at the time of the accidents were moderate to heavy snowfall, snow-covered and icy. Several accidents were also reported on Highway 83 from Seeley Lake to Condon. Snowfall reports: 8 Potomac, 7 Condon, 5 in Bonner and 2 in Seeley Lake.