Fronts

The transition zone between two air masses with distinct temperature and moisture properties is called a front. Fronts can be hundreds of miles long and exist for several days. A cold front indicates that colder air will follow the front's passage; a warm front means that warmer air will follow. On weather maps cold fronts have blue "teeth" and warm fronts have red half-circles, both point in the direction the front is moving. Although fronts are represented on weather maps as lines, they are actually a zone of rapidly changing weather conditions and typically exist at different angles moving upward from the Earth into the atmosphere.