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What is a cyclone?

A cyclone is a large wind system that moves around an area of low atmospheric pressure. It can spread over 500 miles (800 kilometers) in diameter. Low pressure usually develops in large land areas where the air tends to rise. Surrounding air moves toward the low-pressure area and starts to circulate, either clockwise or counterclockwise, depending on whether the cyclone is in the Northern or Southern hemisphere. Cyclones can produce cloudy weather and broad areas of rain and even snow. In the United States, cyclones often are called tornadoes.