Weather front
Cold front

A cold front is located along and on the bounds of the warm side of a tightly packed temperature gradient. On surface analysis charts, this temperature gradient is visible in isotherms and can sometimes also be identified using isobars since cold fronts often align with a surface trough. On weather maps, the surface position of the cold front is marked by a blue line with triangles pointing in the direction where cold air travels and it is placed at the leading edge of the cooler air mass. Cold fronts often bring rain, and sometimes heavy thunderstorms as well. Cold fronts can produce sharper and more intense changes in weather and move at a rate that is up to twice as fast as warm fronts, since cold air is more dense than warm air, lifting as well as pushing the warm air preceding the boundary. The lifting motion often creates a narrow line of showers and thunderstorms if enough humidity is present as the lifted moist warm air condenses. The concept of colder, dense air "wedging" under the less dense warmer air is too simplistic, as the upward motion is really part of a maintenance process for geostrophic balance on the rotating Earth in response to frontogenesis.
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