Earthsky FAQs
Private: What is a front?
07-24-2008 - Earth
Photo: Flickr user .:sandman
During World War I, Norwegian meteorologists noticed that an air mass with certain temperature and humidity characteristics could change rapidly to another distinct air mass with very different characteristics. They named the leading edge of each air mass a “front.” Their use of military terminology was appropriate. The meeting of weather fronts can be violent, spawning thunderstorms and tornadoes.
Both cold and warm air masses are always on the move. Winds high in the atmosphere push them out of the regions where they were formed. For example, in the springtime in North America, cold dry air swooping down from Canada confronts milder, more humid air moving north from the Gulf of Mexico.
When a cold front moves in on a warm air mass, the cold air ploughs under the warm, moist air, forcing it up. And rising unstable air creates storms. Storms pick up their energy from temperature contrasts. That’s why you get such powerful storms in the spring – a time when there’s a big difference between northern cold air and warmer air from the south.