Count the seconds between lightning and thunder, divide by five for miles or three for kilometers. Take cover if the interval is 30 seconds or less.
If you see lightning in the distance and then hear the rumble of thunder, you can tell how far away the storm is. Just count the number of seconds between the lightning and thunder 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 a mile (1.6 km) away. The National Weather Service recommends taking cover if the interval is 30 seconds or less, indicating that the lightning-filled storm is approximately 6 miles (9.7 km) away.
How to stay safe in summer:
This “flash-to-bang” calculation takes into account 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 the air temperature.
For metric measurements, count the number of seconds between seeing lightning and hearing thunder and divide by three to find the distance in miles between you and that storm.
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