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Funnel cloud: A rapidly rotating cone-shaped cloud that extends down from the base of a convective cloud (usually cumulonimbus, the thunderhead), made visible by condensation. If/when it reaches the ground, it is called a tornado.
For up-to-the-minute forecasts by Tom Skilling and additional weather data online, visit chicagotribune.com/weather
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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.
