Dear Tom,
What are the records on humidity? Has there ever been a “0% day”? Is that even possible?
Francis Siby, Naperville, Ill.
Dear Francis,
Relative humidity (RH) readings of 100%, meaning the air is absolutely saturated with water vapor at a given temperature, are common here and at most places around the world. In contrast, very low values of relative humidity are rare, confined almost exclusively to the world’s non-coastal deserts.
Coastal deserts, like those of Chile, receive little rain but are frequently bathed in moist oceanic air. Because some water vapor is always present in air, even in the world’s driest locations, an RH of precisely 0% cannot occur, but 2% has been observed on rare occasions in Death Valley, Calif., and Yuma, Ariz., among other places. Chicago’s lowest RH: 13%.
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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.
