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Answer Man: How can there be 100 percent humidity in the air?

September 13, 2018

Answer Man: I noticed when we got all that rain, even before it started raining, the weather conditions showed 100 percent humidity. How can the air be 100 percent humidity? Wouldn’t 100 percent humidity just be water? — Swimming through life in Rochester

Dear Swimming: It does sound rather absurd that the air would be 100 percent humidity. But I can tell you with 100 percent humility, that’s not what the measurement means.

The relative humidity measures how much water vapor the air can hold at its current temperature without precipitation.

The warmer the air is, the more moisture it can hold, Clint Aegerter, meteorologist with the National Weather Service in La Crosse explains.

That’s why at 40 degrees you still get dry, chapped lips when the relative humidity is 100 percent, but at 80 degrees you feel like you need to wring out your socks.

What it doesn’t mean is that the air is now moisture and you need gills to breathe.

You might also notice the relative humidity can be higher than 100 percent. That’s something called “supersaturation.” It can occur under certain atmospheric conditions and usually means that there is fog or precipitation.

At relatively warm temperatures and at home, the ideal relative humidity for comfort is about 40 percent to 50 percent. Around here in summer, that requires a dehumidifier; in winter, a humidifier.

Here at Answer Man Headquarters, we have something called relative humility, which we try to keep low. We do that with dehumilifiers called facts.

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