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cold front |
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.
leading edge of an advancing mass of relatively cold air. In middle and higher latitudes of both hemispheres cold fronts tend to move toward the Equator and eastward, with the most advanced position right at the ground. At a height of about 1.5 kilometres (1 mile) the front usually lies 80 to 160 kilometres (50 to 100 miles) behind its surface position; thus, its slope is 150 to 1100. The frontal zone, within which the rapid transition from warm to cold air takes place, is narrowest and best defined near the Earth's surface. The cold front is directly related to the polar-front jet stream and usually occurs in close proximity to its core.