Dear Tom,
Why is predicting spring temperatures in Chicago so difficult?
Patrick Walsh, Chicago
Dear Patrick,
Forecasting Chicago’s temperature is difficult any time of the year, but spring temperature forecasts are especially tricky and subject to huge errors.
The main culprit is, of course, Lake Michigan. In spring, the slow-to-warm lake has water temperatures in the 30s and 40s, and being colder than the surrounding land, is a source of high pressure. Since the natural flow of air is from high to low pressure, the wind frequently blows inland, keeping the city chilly.
Another problem in late winter and early spring is snow-covered or frozen ground. Saturday was a perfect example when the cold ground chilled the incoming warm air to condensation, forming fog and resulting in highs in the lower and middle 50s instead of the anticipated middle 60s.
———-
Tom Skilling is chief meteorologist at WGN-TV. His weather forecasts can be seen Monday through Friday on WGN News at noon and 9 p.m.
Write to: ASK TOM WHY, 2501 Bradley Place, Chicago, IL 60618 or asktomwhy@wgntv.com (Mail volume precludes personal response.)
