If you see a lightning strike off in the distance and then hear the rumble of thunder, you can figure out how far away the storm is. Just count the number of seconds that pass between the lightning and the thunder crack, and divide that number by five. The result is the distance in miles. For example, a five-second interval between lightning and thunder indicates that the storm is only one mile (1.6 km) away. The National Weather Service recommends that you head for cover if the interval is 30 seconds or less, which indicates that the lightning-filled storm is about 6 miles (9.7 km) away.
How to stay safe in the summer:
- This “flash-to-bang” calculation takes into account the fact that light travels through the atmosphere much faster than sound.
- Light travels at 186,291 miles per second (299,800 km/s). The speed of sound is only about 1,088 feet per second (332 meters per second), depending on air temperature.
- For metric measurements, count the number of seconds between seeing lightning and hearing thunder, and divide by three in order to find out the distance in kilometers between you and that storm.