Dear Tom,
Is it true that when we hear thunder, lightning must follow and we should head indoors?
John Schuld, New Lenox
Dear John,
It is actually the other way around. Thunder is caused by and always follows lightning. Lightning heats the column of air through which it travels to 50,000(degrees)F or higher, causing it to expand explosively, initiating the shock wave heard as thunder. In this part of the country, thunder is rarely heard beyond about 10 miles from the parent thunderstorm–so if you can hear the thunder, you are definitely within striking reach of the lightning.
Lightning safety experts, among them the University of Illinois-Chicago’s Dr. Mary Ann Cooper, M.D., advise waiting for at least 30 minutes after the last lightning or thunder before resuming outdoor activities. If thunder can still be heard, the storm is too close to safely venture outdoors.
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.
Write to: ASK TOM WHY, 2501 Bradley Pl., Chicago, IL 60618 or asktomwhy@wgntv.com (Mail volume precludes personal response.)
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
