A tornado is a violently rotating column of air that extends from a thunderstorm to the ground. While they can occur almost anywhere, most tornadoes form in the United States and parts of South America, Europe, Asia, Africa, and Australia. Tornadoes typically appear as thin, funnel-shaped clouds less than a few hundred yards wide attached to a larger storm cloud, but can also form in various shapes and sizes. Modern forecasting uses weather radar and storm spotters to issue tornado warnings, helping reduce deaths from these dangerous storms.