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Storm front over Lake Superior (US)
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Courtesy of EPA

Weather Fronts

When a front passes over an area, it means a change in the weather. Many fronts cause weather events such as rain, thunderstorms, gusty winds, and tornadoes. As a cold front passes there may there may be dramatic thunderstorms. At a warm front there may be low stratus clouds.  Usually the skies clear once the front has passed.

A weather front is the transition between two different air masses of different density. Each air mass has its own characteristics such as temperature and humidity. It may extend over hundreds or even thousands of square miles of area. Often there is turbulence where those different air masses come together, which causes clouds and storms.

While many fronts cause storms and clouds, some fronts do not cause dramatic weather events, just a change in the temperature. However, a few fronts start Earth’s largest storms. Tropical waves, fronts that develop in the tropical Atlantic Ocean off the coast of Africa, are able to develop into tropical storms or hurricanes if conditions allow.

Fronts move over time as the air masses move. The direction that fronts move is often guided by high winds such as Jet Streams and also depends on the type of front. Landforms like mountains can also change the path of a front.

There are 4 different types of fronts: cold fronts, warm fronts, stationary fronts, and occluded fronts.

Last modified August 12, 2009 by Lisa Gardiner.

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