An extended period of extreme cold developed over western Montana in early December. It was the coldest air mass in more than 4 years to affect the region. A secondary push of arctic air, much colder than the first, moved into the region late Thursday, Dec. 5 and Dec. 6, which helped to bring gusty winds, and very low wind chills to canyon and mountain gap locations. Flathead Lake and nearby shores saw lake effect snow activity develop on Dec. 4 and continue through Dec. 8, bringing anywhere from a trace up to 10 inches of snow.

Extreme Cold/Wind Chill in WEST GLACIER REGION, MONTANA
From 04-DEC-13 19:30:00 to 08-DEC-13 02:42:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

The Fielding RAWS, located 4.4 miles southwest of Marias Pass, reported air temperatures between -20 and -28 F during the mornings and evenings from 3:42 am MST on Dec. 6, through 2:42 am MST on Dec. 8. The HADS sensor at Marias Pass also measured very cold air temperatures: -27.5 F at 3 am MST Dec. 5, -30.9 F at 7:30 am MST Dec. 6, and -41.2 F at 7:45 am MST Dec. 7. A person from the public located 8 miles southwest of Marias Pass, reported frozen pipes on Dec. 6.

Winter Weather in FLATHEAD/MISSION VALLEYS, MONTANA
From 04-DEC-13 15:00:00 to 08-DEC-13 18:30:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

With arctic air entrenched over western Montana, convergent winds developed over a relatively warm Flathead Lake, allowing for lake effect snow (LES) to develop. Lake temperatures ranged from 32 to 36 degrees Fahrenheit during this event. Depending on where the convergent boundary set up, locations would receive anywhere from a dusting up to 10 inches of snow. During the morning of Dec. 5, a very intense west to east oriented LES band, 1 to 2 miles wide, formed north of Yellow Bay. An estimated 8 to 10 inches fell 1 mile south of Wood's Bay along Hwy-35, especially between mile-marker 18 and 22. An interesting note during this heavy snowfall is that the consistency of the snowflakes were observed to be large dendrites. As a secondary push of colder air moved in later on Dec. 5, the LES band shifted further south and light snow was reported between MM-3 and 5 on Hwy-35 just south of Finley Point. As indicated correctly by the high resolution WRF-ARW model forecast, the LES band became more north to south oriented. It brought up to 3 inches of snow from Polson to Big Arm between MM 57-69 on US-93 through 8:37 am MST on Dec. 6. The LES band continued to affect the Polson area through Dec. 7, bringing less than one inch of snow, which made roads slick. The Polson sheriff reported 2 accidents due to slick conditions at 12:51 pm on Dec. 7. They indicated that the snow was coming down as very fine grains and air temperatures ranged from 0 to -10 F. By the evening of Dec. 7, the LES band had shifted further to the east affecting the east and southeast side of Flathead Lake. A weather spotter located 8 miles north of Finley Point, measured 1 inch of snow between 6 and 6:30 pm MST on Dec. 7. An estimated 8 inches of heavy snow was reported near mile-markers 80-100 on US-93 near Rollins at 5 pm MST on Dec. 8. An estimated 8 inches of snow was reported by MT DOT, 2 miles north of Bigfork at 6:30 pm MST on Dec. 8.

Extreme Cold/Wind Chill in BUTTE / BLACKFOOT REGION, MONTANA
From 03-DEC-13 07:30:00 to 09-DEC-13 02:05:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

The Georgetown Lake MT DOT sensor reported wind chill values between -20 and -31 F. The coldest air temperature reported was -22 F at 12:25 am MST on Dec. 8. The MT DOT sensor located 7 miles north-northwest of Avon on MT-141, reported wind chill values between -20 to -45 F from Dec. 3-9. The -45 F wind chill occurred at 1:59 am MST on Dec. 7, with a wind speed of 11 mph and air temperature was -22.7 F. The Bert Mooney Airport ASOS recorded its coldest wind chill of -35 F at 1:53 am MST on Dec. 7.

Extreme Cold/Wind Chill in WEST GLACIER REGION, MONTANA
From 04-DEC-13 21:38:00 to 08-DEC-13 02:16:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

The Essex MT DOT sensor reported wind chill values between -20 and -33 F, with an average wind speed of 9 mph through 11:22 am MST Dec.5.  The peak wind during that time was 17 mph.  It also measured -20 to -32 F wind chill values from 9:16 pm MST Thursday Dec. 5 through 11:31 am MST Friday Dec. 6, with an average wind speed of 7 mph.  The peak wind was 18 mph.  It also reported -20 to -49 F wind chill values from 3:16 pm MST Dec. 6 through 12:20 pm MST Dec. 7, with an average wind speed of 10 mph.  The -49 F wind chill occurred at 7:58 am MST on Dec. 7 with a wind speed of 19 mph. It reported air temperatures between -20 and -22 F from 8:13 pm MST Dec. 7 through 2:16 am MST Dec. 8. The prevailing wind direction throughout this event was from the southeast.

Extreme Cold/Wind Chill in LOWER CLARK FORK REGION, MONTANA
From 06-DEC-13 03:53:00 to 08-DEC-13 08:26:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

The Mullan Pass sensor reported -20 to -34 wind chill values with an average wind speed of 8 mph. The -34 F value was observed at 6:53 MST on Dec. 7 when the air temperature was -13 F and the wind speed was 12.7 mph.

Extreme Cold/Wind Chill in KOOTENAI/CABINET REGION, MONTANA
From 06-DEC-13 04:00:00 to 08-DEC-13 02:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

The Stillwater RAWS at 3,116 ft., located 1.1 mile southeast of Olney, reported air temperatures between -20 and -31 F mainly during the late evening and morning hours during this time period. The coldest value of -31 F occurred at 8 am MST on Dec. 7, which happens to be the same temperature recorded by the Olney COOP, and was a record minimum for the day. The Boorman RAWS at 3,963 ft., located 3 miles northwest of Marion reported air temperatures between -20 and -25 F between Dec. 6-8.

Extreme Cold/Wind Chill in MISSOULA / BITTERROOT VALLEYS, MONTANA
From 06-DEC-13 06:45:00 to 07-DEC-13 14:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

The Missoula International Airport reported wind chill values between -20 and -28 F with an average wind speed of 16 mph. During the morning of Dec. 7, the wind chill values could have ranged between -30 and -35 F across eastern Missoula, especially by Hellgate Canyon where wind speeds were a little stronger than by the airport. Thousands of people attended a championship football game at the University of Montana football stadium, while wind chill values possibly fluctuated between -15 and -20 F at times during the early afternoon on Dec. 7.

Extreme Cold/Wind Chill in POTOMAC / SEELEY LAKE REGION, MONTANA
From 05-DEC-13 02:00:00 to 08-DEC-13 00:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

The Pistol Creek RAWS at 6,043 ft., reported wind chill values between -20 and -39 F while wind speeds averaged around 7 mph. It measured the -39 F reading at 12:41 am MST on Dec. 7 with a speed of 11 mph. The Greenough Hill MT DOT sensor measured air temperatures from -20 to -22 F between 5 am and 9:08 am MST on Dec. 7. It also reported an air temperature of -20 F between 11:08 pm Dec. 7 and 2:32 am MST on Dec. 8. The Snowbowl ski resort cancelled their opening day, Friday, Dec. 6, and also Saturday, Dec. 7, due to the extreme cold.

Extreme Cold/Wind Chill in FLATHEAD/MISSION VALLEYS, MONTANA
From 06-DEC-13 04:55:00 to 07-DEC-13 10:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

The Glacier Park International Airport ASOS reported wind chill values between -20 and -30 F, while north-northeast winds averaged around 15 mph. Both the City of Columbia Falls and Polson cancelled their Parade of Lights Dec. 6 due to the cold. The Bigfork Area Chamber of Commerce cancelled the Annual Magical Holiday Parade that was planned to occur on Dec. 7.