ASK TOM: Largest 24-hour temperature change in the U.S.

Dear Tom,

What is the greatest temperature difference ever recorded between a daytime high and nighttime low temperature, and what creates such extreme conditions?

–John Wilson, Huntington Beach, Calif.
Dear John,

The largest temperature changes within a 24-hour period in the United States occur in the High Plains of Colorado, Wyoming and Montana in the immediate lee of the Rocky Mountains — those areas subject to chinook winds. On occasion, mild Pacific air surges over the Rockies and violently descends onto the Plains, compressing and warming and displacing preexisting bitterly cold arctic air. Such was the case On Jan. 14-15, 1972, in Loma, Montana, an observer for the National Weather Service recorded a 24-hour temperature rise of 103 degrees, from 54 degrees below zero to 49 degrees above zero.

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