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Weather Talk: Most people mistaken on how humidity’s quantified

Everybody knows about humidity in the summertime.  But most people are mistaken about how humidity is quantified. 

Relative humidity is expressed as a percentage. But it is not a percentage of water vapor in the air. The percentage of water vapor in the air is very, very small – usually around 1 to 3 percent. So it is useless to use this as a gauge. Instead, relative humidity can be expressed as a percentage of saturation. But people are usually not aware that this percentage of saturation is not the same as a percentage by volume.

Relative humidity is a reflection of water vapor and air temperature. Therefore 80 percent relative humidity on a cool day means something entirely different than on a hot day.

Meteorologists use the dew point temperature as a way to gauge humidity in terms of human discomfort. The higher the dew point, the more sticky people feel. Dew points in the 70s indicate sweltering summer humidity.

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