Dear Tom,
A couple years ago, we had some very light rain in Western Springs in the afternoon. I went outside to pick up the kids’ toys and looked up, and a large part of the sky overhead was clear. I have always wondered about this.
Will H., Western Springs
Dear Will,
Sometimes the clouds that produce rain are small and moving rapidly, and this probably occurred in the situation you have described. Rain fell from the cloud, but by the time the drops reached the ground, the cloud had moved on. Small raindrops descend relatively slowly, at speeds of 10- 15 feet per second. If the cloud from which they were falling was based at 5,000 feet–a typical height–more than eight minutes would elapse before the raindrops reached the ground. That is sufficient time for the cloud to move away from directly overhead.
———-
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.
