Dear Tom,
As a boy many years ago, I remember that there would sometimes be flashes in the evening sky on a hot, clear summer night. My grandparents called it heat lightning. Is this term correct, and what would cause it?
Jay Dralle, East Moline, Ill.
Dear Jay,
“Heat lightning” is real, but it is not a discrete phenomenon.
It is always regular, storm-generated lightning, except that it is so far away that its thunder cannot be heard and the cumulonimbus cloud producing it cannot be seen.
Thunderstorm tops often exceed heights of 50,000 feet, allowing the luminosity of lightning in the upper portions of the storm to be seen 100 miles or more if intervening clouds do not block the view. Thunder, the sound generated by lightning, rarely carries beyond 20 miles.
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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.
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
