A very cold arctic air mass from the north strengthened and spread over the region. It's persistence and often clear skies, along with even a little bit of wind led to dangerous wind chill values across most of northeast Montana for more than a week.

Cold/Wind Chill in CENTRAL AND SE PHILLIPS, MONTANA
From 10-FEB-21 00:15:00 to 14-FEB-21 08:35:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

At the Malta airport AWOS site (KM75), although conditions were not quite as bad during the daytime, night-time temperatures below -20 and breezy winds created wind chills of at least -40 or worse each night from the morning of the 8th through the morning of the 14th.  The peak wind chill of -50 was recorded at 1:15 AM on the 12th.

Cold/Wind Chill in LITTLE ROCKY MOUNTAINS, MONTANA
From 10-FEB-21 06:23:00 to 14-FEB-21 08:11:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

At the Malta South US-191 DOT site (MTMAL), temperatures in the teens and 20s below zero and breezy winds created wind chills of -40 or worse from the morning of the 10th into the morning of the 14th.  The peak wind chill of -49 was recorded at 1:54 AM on the 11th.

Cold/Wind Chill in GARFIELD, MONTANA
From 09-FEB-21 19:37:00 to 14-FEB-21 18:48:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

For multiple sites across Garfield County, temperatures in the teens and 20s below zero and breezy winds created wind chills of -40 or worse beginning as early as the evening of the 9th and lasting as long as the evening of the 14th.  The peak wind chill of -54 was recorded at 6:48 PM on the 14th at the Jordan airport ASOS site (KJDN).

Cold/Wind Chill in NORTHERN VALLEY, MONTANA
From 07-FEB-21 21:44:00 to 14-FEB-21 07:44:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

At the Bluff Creek RAWS site (BLUM8), temperatures in the teens and 20s below zero and breezy winds created wind chills of -40 or worse from the night of the 7th into the early morning of the 14th.  The peak wind chill of -56 was recorded at 6:44 AM on the 13th.

Cold/Wind Chill in CENTRAL AND SOUTHERN VALLEY, MONTANA
From 07-FEB-21 21:10:00 to 14-FEB-21 06:53:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

For multiple sites across central and southern Valley County, temperatures in the teens and 20s below zero and breezy winds created wind chills of -40 or worse beginning as early as the night of the 7th and lasting as long as the early morning of the 14th. The peak wind chill of -52 was recorded at 2:26 AM on the 14th at the Saco US-2 DOT site (MTSCO).

Cold/Wind Chill in DANIELS, MONTANA
From 05-FEB-21 22:01:00 to 14-FEB-21 04:46:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

At the Navajo MT-5 DOT site (MTRED), temperatures in the teens and 20s below zero and breezy winds created wind chills of -40 or worse from the night of the 5th into the early morning of the 14th. The peak wind chill of -53 was recorded from 12:01 AM to 1:34 AM on the 12th.

Cold/Wind Chill in PRAIRIE, MONTANA
From 09-FEB-21 02:08:00 to 14-FEB-21 04:15:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: RAWS

For multiple sites across Prairie County, temperatures below -20 and breezy winds created wind chills of at least -40 or worse beginning in the early morning of the 9th and lasting into the early morning of the 14th. The peak wind chill of -49 was recorded from 2:08 AM to 3:08 AM on the 12th at the Big Sheep Mountain RAWS site (LCFM8).

Cold/Wind Chill in EASTERN ROOSEVELT, MONTANA
From 06-FEB-21 00:44:00 to 06-FEB-21 18:55:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

For multiple sites across eastern Roosevelt County, temperatures below -20 and breezy winds created wind chills of at least -40 or worse beginning in the early morning of the 6th and lasting into the evening of the 13th. The peak wind chill of -49 was recorded from  4:55 AM  to 5:10 AM on the 12th at the Culbertson airport mesonet site.

Cold/Wind Chill in RICHLAND, MONTANA
From 06-FEB-21 01:54:00 to 14-FEB-21 07:56:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

For multiple sites across Richland County, temperatures below -20 and breezy winds created wind chills of at least -40 or worse beginning as early as the early morning of the 6th and lasting as late as the morning of the 14th. The peak wind chill of -51 was recorded both at 3:54 AM and 6:55 AM on the 12th at the Sioux Pass MT-16 DOT site (MTSOO).

Cold/Wind Chill in WESTERN ROOSEVELT, MONTANA
From 06-FEB-21 00:01:00 to 14-FEB-21 07:37:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

For multiple sites across western Roosevelt County, temperatures in the teens and 20s below zero and breezy winds created wind chills of -40 or worse beginning as early as the early morning of the 6th and lasting as long as the early morning of the 14th. The peak wind chill of -52 was recorded at 3:46 AM on the 12th at the McDonalds MT-13 DOT site (MTMCD).

Cold/Wind Chill in SHERIDAN, MONTANA
From 05-FEB-21 21:27:00 to 14-FEB-21 07:46:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

For multiple sites across Sheridan County, temperatures in the teens and 20s below zero and breezy winds created wind chills of -40 or worse beginning as early as the night of the 5th and lasting as long as the early morning of the 14th. The peak wind chill of -55 was recorded from 1:13 AM to 1:23 AM on the 12th at the Comertown Turn-OFF MT-5 DOT site (MTCOM).

Cold/Wind Chill in MCCONE, MONTANA
From 06-FEB-21 05:59:00 to 14-FEB-21 08:40:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

For multiple sites across McCone County, although initially in a more isolated way,  temperatures below -20 and breezy winds created wind chills of at least -40 or worse beginning as early as the morning of the 6th and lasting as late as the morning of the 14th. The peak wind chill of -62 was recorded at 4:55 AM on the 14th at the Circle Town County Airport mesonet site (K4U6).

Cold/Wind Chill in DAWSON, MONTANA
From 08-FEB-21 06:56:00 to 15-FEB-21 04:19:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

For multiple sites across Dawson County, although initially in a more isolated way, temperatures below -20 and breezy winds created wind chills of at least -40 or worse beginning as early as the morning of the 8th and lasting as late as the early morning of the 15th. The peak wind chill of -54 was recorded from 5:39 AM to 7:25 AM on the 12th at the Lindsay Divide MT-200 DOT site (MTLND).

Cold/Wind Chill in WIBAUX, MONTANA
From 08-FEB-21 22:47:00 to 14-FEB-21 07:35:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

At the Beaver Hill I-94 DOT site (MTBVR), temperatures below -20 and breezy winds created wind chills of at least -40 or worse from the night of the 8th into the morning of the 14th. The peak wind chill of -51 was recorded from 4:33 AM to 6:33 AM on the 12th.