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A front is the boundary between two air masses.


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A front is a zone that separates two air masses with different characteristics in the troposphere. The main difference between the two air masses is temperature.

There are three main types of front:

A front that moves very slowly, even stopping, becomes a stationary front. In this case it is the direction of high-altitude winds in relation to the front that determines whether the front moves or not. If the high-altitude winds are blowing perpendicularly to the front on the ground, they keep the front moving. But if the high-altitude winds change direction and blow parallel to the front, they can no longer exert pressure on the front so it slows down and can become stationary.

Fronts associated with depressions circulate in a westerly stream. On ground weather maps warm fronts are shown by a red line with semicircles, cold fronts by a blue line with triangles and occlusions by a purple line with semicircles as well as triangles. Stationary fronts are shown by a red and blue line with semicircles and triangles (a mix of cold and warm fronts).