Dear Tom,
What is the rule for determining the distance of lightning when you hear its thunder?
John Warner, Brookfield

Dear John,

It is a simple thing to do. Count the number of seconds that pass between the flash of lightning and the crack of thunder that follows it: then divide that number by five. The result gives the distance in miles between you and the closest part of the lightning bolt. The calculation is based on the speed of sound in air. Lightning is essentially seen at the instant it occurs, even from a considerable distance. Sound travels at around 1100 ft/second so the sound of thunder travels roughly 1 mile every 5 seconds. Lightning kills about 50 people per year in the United States and can strike several miles from the main precipitation core of a thunderstorm.