Dear Tom,
When can I be assured the danger of frost and freezing temperatures in Chicago is past for good?
— Jeffrey Rayner, Chicago
Dear Jeffrey,
Light frost can form on plant leaves on a clear, calm night even when air temperatures a few feet above the ground are as high as 38 degrees. A heavy, killing frost usually requires a temperature of 32 degrees or lower.
Because overnight temperatures on a chilly spring night can, in extreme cases, vary by 20 degrees across the Chicago area, it is difficult to pin down an exact date. It depends on your location.
Here are some guidelines: Near the lake, light frost (38 degrees) has never occurred beyond May 31; heavy frost (32 degrees) never beyond May 14. Two to 6 miles inland, the corresponding dates are June 4 and May 13; 7 to 15 miles inland, June 22 and May 29; farther inland, add seven days.
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Write to: ASK TOM WHY, 2501 Bradley Pl., Chicago, IL 60618 or: asktomwhy@wgntv.com
Weather Report is prepared by the WGN-TV Weather Center, where Tom Skilling is chief meteorologist. His forecasts can be seen Monday through Friday on WGN News at noon, 5:55 p.m. and 9 p.m.
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
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