Dear Tom,
A friend in Iraq told me that, besides a lot of heat and dust, they had a lightning storm–no rain; no thunder; just lightning. How can you have lightning and no thunder?
–Mary Abuja, San Diego
Dear Mary,
Thunder is always a byproduct of lightning, but sometimes we are too far away to hear it.
A lightning spark can heat the air through which it passes to 54,000 degrees practically instantaneously. Such extreme heating causes air to expand explosively, followed immediately by cooling and rapid contraction. That physical process sets up sound waves that blast outward, and we hear them as thunder.
However, thunder dampens quickly as it spreads and it rarely carries more than 15 miles from its source, whereas lightning bolts are often visible at distances beyond 50 miles if intervening clouds are not present.
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Write to: ASK TOM WHY, 2501 Bradley Pl., Chicago, IL 60618 or: asktomwhy@wgntv.com
Weather Report is prepared by the WGN-TV Weather Center, where Tom Skilling is chief meteorologist. His forecasts can be seen Monday through Friday on WGN News at noon, 5:55 p.m. and 9 p.m.
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