Dear Tom,
A friend scoffs when I mention that we’re getting to the season for lake-effect rain. I know there is such a thing, but I need your help here.
Tim Zimmer
Dear Tim,
Lake-effect rain is a bona-fide weather phenomenon and it does occur in the Chicago area, but only rarely.
The development of lake-effect precipitation requires that the temperature of air traversing the lake be at least 20(degrees) cooler than the lake water temperature. A differential of that magnitude allows for sufficient heat and moisture transfer (from lake to overlying air) to destabilize the air and generate clouds and precipitation.
Because summer air temperatures are almost never 20(degrees) cooler than lake water temperatures, we seldom see lake-effect rain. It usually occurs only during the autumn season’s first strong cold outbreaks in October and November.
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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.
