ASK TOM: Warm fronts and cold fronts in nontechnical terms

Dear Tom,

Can you describe warm fronts and cold fronts in nontechnical terms?

— Jacob Vestal


Dear Jacob,

On a weather map, a “front” is the boundary between two air masses. Fronts are often a few hundred miles in length, sometimes more than a thousand miles. In width, a frontal boundary zone ranges from a few miles to about 50 miles.

Air temperature and moisture content are usually the two characteristics that cause air masses to differ from one another. In the most typical case, one air mass is colder and drier than the other.

A front can be stationary, but it usually moves, often at speeds of 20 to 35 mph, rarely above 45 mph. When a frontal zone is moving in such a way that colder air is replacing warmer air, it’s called a cold front. When warmer air is replacing colder air, it’s called a warm front.