Front over Lake Superior (US) Click on image for full size (42 Kb) Courtesy of EPA

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. At 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 a border between two different air masses at the Earth’s surface. Each air mass has its own characteristics such as temperature and humidity. Where two different air masses come in contact, the line between them is a front. Often there is turbulence where those different air masses come together. The turbulence can cause 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. 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.