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What makes a thunderstorm considered "severe"?

A thunderstorm is classified as SEVERE where it contains one or more of the following criteria:

  • Hail ¾ inch or greater
  • Winds gusting in excess of 58 mph
  • A tornado

A typical thunderstorm is 15 miles in diameter and lasts an average of 30 minutes. There are 1800 thunderstorms at any given moment around the world. Of the estimated 100,000 thunderstorms that occur in the United States, about 10 percent are classified as SEVERE.