Severe Thunderstorms – Introduction


Thunderstorms affect relatively small areas when compared with hurricanes and winter storms. The typical thunderstorm is 15 miles in diameter and lasts an average of 30 minutes. Despite their small size, ALL thunderstorms are dangerous!

Of the estimated 100,000 thunderstorms that occur each year in the United States, about 10 percent are classified as severe (one that produces hail at least an inch or larger in diameter, has winds gusting in excess of 50 knots (57.5 mph), or produces a tornado).[1]

The Hazards of Severe Thunderstorms

Although all thunderstorms are dangerous, every thunderstorm produces lightning. While lightning fatalities have decreased over the past 30 years, lightning continues to be one of the top three storm-related killers in the United States. In 2010, there were 29 fatalities and 182 injuries from lightning.

Other associated dangers of thunderstorms include tornadoes, strong winds, hail and flash flooding. Flash flooding is responsible for more fatalities – more than 140 annually – than any other thunderstorm-associated hazard.[2]

When are where in the U.S. are thunderstorms most likely?

Thunderstorms are most likely in the spring and summer months and during the afternoon and evening hours, but they can occur year-round and at all hours.

Thunderstorms occur along the Gulf Coast and across the southeastern and western states, most thunderstorms occur during the afternoon.

Thunderstorms frequently occur in the late afternoon and at night in the Plains states. However, no place in the United States is completely safe from the threat of severe weather.[3]


  1. NOAA National Severe Storms Laboratory (NSSL):
  2. – Thunderstorms and Lightning:
  3. NOAA National Severe Storms Laboratory (NSSL):
  4. Image Source: [Accessed: Jan 18, 2017]