Lightning quickly heats the air causing it to expand, which produces the sound of thunder. Sound travels approximately 1 mile in 5 seconds. Knowing D = rt, how far away is a thunderstorm when you notice a 3- second delay between the flash of lightning and the sound of thunder? Lightning quickly heats the air causing it to expand , which produces the sound of thunder . Sound travels approximately 1 mile in 5 seconds . Knowing D = rt , how far away is a thunderstorm when you notice a 3 second delay between the flash of lightning and the sound of thunder ?