Dear Tom,
I once observed cirrus, stratus and cumulus clouds moving in three different directions. Besides the wind factor, what could cause that?
Kris Brummel, Yorkville, Ill.
Dear Kris,
Wind is the causative factor–because clouds move with the wind, but there are exceptions. Some thunderstorms, for example, remain stationary while the winds in which they are immersed sweep around them. The three cloud types that you mentioned exist at very different elevations in the atmosphere. Your observation gives visual proof that wind direction almost always changes with height. Stratus are low clouds, often occurring below 1,000 feet. Cumulus, typically with bases 2-5 thousand feet aloft, move with winds at that level. Cirrus are high-level clouds, at 20-50 thousand feet.
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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.
