The National Weather Service considers a thunderstorm severe if the any of the following happens:
A SEVERE THUNDERSTORM WATCH means conditions are favorable for the development of thunderstorms that may turn severe.
A SEVERE THUNDERSTORM WARNING means severe weather is in the area, and you need to take safety precautions.
Here are some safety tips for when a thunderstorm is approaching:
At any one moment nearly 1800 thunderstorms are occurring around the world and that amounts to over 16 million storms in a year. In the United States, it is estimated 100,000 thunderstorms occur each year with only about 10,000 actually reaching severe limits. A typical thunderstorm is 15 miles in diameter and lasts for about 30 minutes.