Dear Tom,
With the cool August in progress, does this mean the odds of an early frost increase?
Jim McCormick, McHenry, Ill.
Dear Jim,
We’re experiencing a near record-cool August–4.2(degrees) below normal through the 26th–but gardeners take note: That’s not a reliable predictor of future frost occurrences. A computer scan of Chicago’s late summer and autumn temperatures yields that surprising verdict.
Using 76 years (1928-2003) of temperatures as registered at Midway Airport, we identified every year whose August was at least 3.5(degrees) below normal–six of them. In those six years, the average date of the first occurrence of 35(degrees) or lower (scattered frost is likely when minimum temperatures descend to the middle 30s) was October 13. That date precedes the average first date of 35(degrees) in all years–October 15–by only two days.
———-
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.
Write to: ASK TOM WHY, 2501 Bradley Pl., Chicago, IL 60618 or asktomwhy@wgntv.com (Mail volume precludes personal response.)
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
