· Extratropical cyclones form between two air masses. Specifically, they form between Ferrel and polar cells. These areas are also known as polar fronts. They move eastward, and are able to generate large frontal storms where warm and cold fronts meet.
· Extratropical storms are most common in the winter seasons of each hemisphere. This is due to large differences in temperature and density across the polar front.
· Tropical cyclones are large masses of warm, humid, rotating air. Unlike the extratropical cyclones, they form within a single air mass. They tend to move westward.
· Both tropical and extratropical cyclones are large rotating storms with masses of low pressure air in which winds converge and lift. They move counterclockwise in the Northern Hemisphere and clockwise in Southern Hemisphere.