Dear Tom,
We have noticed that humidity readings in Florida are usually lower than in Illinois, but it is much more humid there. Does it have to do with air density?
Teresa Vander Biezen
Dear Teresa,
Air’s density is not a factor in how humid it feels. Surprisingly, humid air is actually less dense than dry air. Airborne moisture –water vapor–is the key: The more water vapor there is in air, the more humid it feels.
However, warm air can hold much more water vapor than cool air (twice as much at 97(degrees) than at 75(degrees), for example). That means the relative humidity (the percent saturation of air) will usually be lower at high temperatures because so much moisture is required to saturate hot air, and 97(degrees) in Florida with a “low” humidity of 50% represents the same moisture content as 75(degrees) in Chicago with 100% humidity.
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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.
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.
