A long cloud formed over the eastern side of the Bitterroot Valley Monday, September 12.

The shelf cloud stretched over the Sapphire Mountains at sunset and was caught by photographer Mike Daniels.

Also known as a roll cloud, this unusual formation was probably part of the cold front that passed through Montana Monday, bringing high winds to many areas.

Following the passage of the front, the night skies over the Bitterroot cleared and the temperature dropped below freezing.

Roll cloud September 12 in Bitterroot Valley. (Mike Daniels, Townsquare Media)