Thunderstorms pose a safety hazard in several ways. Lightning is the most dangerous part of a thunderstorm, and it kills more people than hurricanes and tornadoes combined. Thunderstorms produce heavy rain, which can cause flash flooding. The strong winds from a thunderstorm can also cause widespread damage. Each of these components requires specific precautions to minimize their danger.
A thunderstorm typically has a diameter of 15 miles and lasts for 30 minutes, which is much smaller than a hurricane or winter storm. The National Weather Service places specific criteria on a severe thunderstorm. These include thunderstorms that produce hail with a diameter of at least ¾ inch, wind gusts of at least 58 mph or a tornado. Severe thunderstorms comprise about 10 percent of all thunderstorms.
The NWS recommends that you stay indoors for 30 minutes after the last clap of thunder when you hear thunder less than 30 seconds after the lightning. This rule is known as the 30/30 lightning safety rule.
Avoid taking emergency shelter in structures that are vulnerable to high winds, such as a mobile home. Outdoors shelters such as sheds, pavilions and golf’s typically will not protect you from flying debris and lightning. Avoid and report downed power lines. Bring pets and livestock under shelter to protect them during hailstorms.