The previous record at the Mount Washington Observatory in New Hampshire was minus 31 degrees and was set in 1933.
The observatory has posted a Facebook video showing weather observer Adam Gill emptying a pitcher of boiling water into the air, where it immediately turns to snow in the cold and hurricane-force winds.
Bitter cold weather has taken hold of much of the northern United States. Wind chill advisories or warnings were in effect for much of New England, northern Pennsylvania and New York on Thursday.
Forecasters warn of hypothermia and frostbite from arctic air settling in over the central U.S. and spreading east.