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the boundary line between a warm air mass and the cold air pushing it from beneath and behind as it moves

the line on the earth's surface where the cold front meets it

The forward edge of an advancing mass of cold air that pushes under a mass of warm air. Cold fronts often cause precipitation; water vapor in the rising warm air condenses and forms clouds, often resulting in heavy rain, thunderstorms, hail, or snow. Winter cold fronts can cause temperatures to drop significantly. Summer cold fronts reduce humidity as drier, cooler air displaces the humid, warmer air. On a weather map, a cold front is depicted as a blue line with triangles that point in the direction in which the cold air is moving.

Compare occluded front warm front See illustration at front