Although thunderstorms affect relatively small geographical areas, they are all dangerous and capable of producing tornadoes, strong winds, hail, wildfires and flash flooding. A typical thunderstorm lasts an average of 30 minutes and is 15 miles in diameter. Ten percent of 100,000 thunderstorms that occur in the U.S. annually are classified as severe. The National Weather Service considers a thunderstorm severe if it produces hail at least ¾-inch in diameter, winds of 58 mph or stronger, or a tornado.
A serious threat with any thunderstorm is the risk of lightning. Lightning's risk to individuals and property is increased because of its unpredictability, which emphasizes the importance of preparedness. It often strikes outside of heavy rain and may occur as far as 10 miles away from any rainfall. In the United States, lightning kills 300 people and injures 80 on average, each year. Most lightning deaths and injuries occur when people are caught outdoors in the summer months during the afternoon and evening.
- Remember the 30/30 Lightning Safety Rule: Go indoors if, after seeing lightning, you cannot count to 30 before hearing thunder. Stay indoors for 30 minutes after hearing the last clap of thunder.
- Familiarize yourself with the terms that are used to identify a thunderstorm hazard
- A thunderstorm watch means there is a possibility of a thunderstorm in your area.
- A thunderstorm warning means a thunderstorm is occurring or will likely occur soon. If you are advised to take shelter, do so immediately.
- Prepare your home in order to minimize or prevent damage or personal injury. This includes:
- Removing dead or rotting trees and branches that could fall and cause injury or damage during a severe thunderstorm.
- Securing outdoor objects that could blow away or cause damage.
- Shutter windows and securing outside doors. If shutters are not available, close window blinds, shades or curtains.