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Airmass thunderstorm: A type of thunderstorm, not associated with fronts or storm systems, that forms in mid or late afternoon in an air mass that has become unstable because of low-level heating by the sun.
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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.
