A frigid arctic air mass combined with a tight surface pressure gradient to allow very cold winds to spread across northeast Montana.

Extreme Cold/Wind Chill in MCCONE, MONTANA
From 31-JAN-13 06:20:00 to 31-JAN-13 07:07:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

A few observation sites reported wind chills around negative 40 for about one hour.

Extreme Cold/Wind Chill in RICHLAND, MONTANA
From 31-JAN-13 02:09:00 to 31-JAN-13 08:55:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

The Sioux Pass DOT site reported wind chills at or below negative 40 for about 6 hours.

Extreme Cold/Wind Chill in DAWSON, MONTANA
From 31-JAN-13 03:28:00 to 31-JAN-13 08:02:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

The Beaver Hill I-94 DOT site reported wind chills at or below negative 40 for about 4 hours.

Extreme Cold/Wind Chill in WIBAUX, MONTANA
From 31-JAN-13 03:28:00 to 31-JAN-13 08:02:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

The Beaver Hill I-94 DOT site reported wind chills at or below negative 40 for about 4 hours.

Extreme Cold/Wind Chill in NORTHERN VALLEY, MONTANA
From 30-JAN-13 23:00:00 to 31-JAN-13 02:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

The RAWS site at Bluff Creek reported wind chills at or below negative 40 for about 3 hours.

Extreme Cold/Wind Chill in SHERIDAN, MONTANA
From 30-JAN-13 06:23:00 to 31-JAN-13 13:03:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Reports of wind chills at or below negative 40 were common with the longest stretch of frigid wind chills being reported at the Comertown DOT site.

Extreme Cold/Wind Chill in NORTHERN PHILLIPS, MONTANA
From 30-JAN-13 23:00:00 to 31-JAN-13 03:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Automated observations in this area were unavailable, but the AWOS site at Val Marie, just across the Canadian border reported wind chills at or below negative 40 for about 4 hours.  And, the stations just east in Valley County reported wind chills of 40 below zero for more than 3 hours.

Extreme Cold/Wind Chill in CENTRAL AND SOUTHERN VALLEY, MONTANA
From 31-JAN-13 02:53:00 to 31-JAN-13 04:53:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

ASOS observations at the Glasgow airport recorded wind chills at and below 40 below zero.

Extreme Cold/Wind Chill in WESTERN ROOSEVELT, MONTANA
From 30-JAN-13 07:49:00 to 31-JAN-13 10:43:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Reports of wind chills at or below negative 40 were common with the longest stretch of frigid wind chills being reported at the McDonalds DOT site.

Extreme Cold/Wind Chill in EASTERN ROOSEVELT, MONTANA
From 30-JAN-13 21:23:00 to 31-JAN-13 11:54:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Cooperative observer located 4 miles east of Bainville reported wind chills near or below negative 40 for about 14 hours.

Extreme Cold/Wind Chill in DANIELS, MONTANA
From 30-JAN-13 20:00:00 to 31-JAN-13 12:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Wind chills at or below negative 40 were observed just across the Canadian border and at the Navajo DOT site at Flaxville on and off over these two days.