A stalled ridge of strong high pressure over the region allowed high temperatures to climb well into the triple digits for many locations for multiple days.  Relative humidity values increased enough to make conditions unusually humid. These conditions combined to warrant the issuance of this area's first excessive heat warning.

Excessive Heat in DAWSON, MONTANA
From 11-AUG-18 11:00:00 to 12-AUG-18 17:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

During the afternoon hours of the 11th and 12th at the Glendive airport, high temperatures ranged from 102 to 106 degrees while dew points ranged from the mid 40s to mid 50s.  Even though this resulted in relative humidity values dropping down into the teens, the unusually hot temperatures and stagnant winds added stress to those with heat sensitivities.

Excessive Heat in GARFIELD, MONTANA
From 10-AUG-18 11:00:00 to 11-AUG-18 17:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

During the afternoon hours of the 10th and 11th at the Jordan airport, high temperatures ranged from 103 to 105 degrees while dew points ranged from the upper 30s to lower 40s. Even though this resulted in relative humidity values dropping down into the teens, the unusually hot temperatures and stagnant winds added stress to those with heat sensitivities.

Excessive Heat in CENTRAL AND SOUTHERN VALLEY, MONTANA
From 10-AUG-18 11:00:00 to 11-AUG-18 17:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

During the afternoon hours of the 10th and 11th at the Glasgow airport, high temperatures reached up to 107 degrees while dew points ranged from the mid 30s to mid 40s.  Even though this resulted in relative humidity values dropping below ten percent, the unusually hot temperatures and stagnant winds added stress to those with heat sensitivities.

Excessive Heat in WESTERN ROOSEVELT, MONTANA
From 09-AUG-18 11:00:00 to 11-AUG-18 17:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

During the afternoon hours of the 9th through the 11th at the Wolf Point airport, high temperatures ranged from 102 to 107 degrees while dew points ranged from the upper 30s to mid 40s.  Even though this resulted in relative humidity values dropping to around ten percent, the unusually hot temperatures and stagnant winds added stress to those with heat sensitivities.

Excessive Heat in RICHLAND, MONTANA
From 11-AUG-18 11:00:00 to 12-AUG-18 17:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

During the afternoon hours of the 11th and 12th at the Sidney airport, high temperatures reached up to 105 degrees while dew points ranged from the mid 40s to mid 50s.  Even though this resulted in relative humidity values dropping down into the teens, the unusually hot temperatures and stagnant winds added stress to those with heat sensitivities.

Excessive Heat in DANIELS, MONTANA
From 10-AUG-18 11:00:00 to 11-AUG-18 17:00:00 (MST-7)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

During the afternoon hours of the 10th and 11th at the Scobey airport, high temperatures reached 103 degrees while dew points ranged from the lower 40s to lower 50s.  Even though this resulted in relative humidity values dropping down into the teens, the unusually hot temperatures and stagnant winds added stress to those with heat sensitivities.