What Is a Tornado?

How the the National Severe Storms Laboratory defines a tornado.

By Susan Fotovich McCabe

The National Severe Storms Laboratory (NSSL) defines a tornado as a “violently rotating column of air extending from a thunderstorm to the ground.” With wind speeds that reach 250 miles per hour or more, a tornado’s wake of destruction can measure in excess of 1 mile wide and 50 miles long.

The NSSL, which works to improve the lead time and accuracy of severe weather warnings and forecasts, reports that tornadoes are most likely to occur between 3 and 9 p.m., but have been known to happen at all hours of the day and night. And while they happen in many parts of the world, tornadoes most frequently occur in the United States, east of the Rocky Mountains during the spring and summer months. On average, approximately 800 tornadoes are reported nationwide each year, and are to blame for 80 deaths and more than 1,500 injuries annually.

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