High humidity can be a real 'drag'

MANHATTAN, Kan. - The phrase is used over and over again - "it's not the heat, it's the humidity." But what exactly does that mean?

Relative humidity actually is a relative measure, said Mary Knapp,

State of Kansas climatologist. The amount means it varies with the temperature.

This elusive value, however, can be a day-to-day concern. Relative humidity can affect humans' mood and well-being.

"The effects are worst when it's high or low," Knapp said. "All relative humidity is, though, is the amount of air-borne water vapor needed to reach the saturation point - in other words, to condense and become rain, snow or fog.

"The warmer the temperature is, the more moisture the condensing process requires. During summer, 50 percent relative humidity means a whole lot more water than it does in the winter."

Indoor, as well as outdoor air temperatures can affect its effects, she said.

Most air conditioners, for example, take in hot summer air. Because they cool it, they also raise its relative humidity.

"As a result, people may develop a 'wet' cough, even when the relative humidity outdoors isn~t too bad. Other typical effects of high humidity can be irritability, red eyes and a general feeling of tiredness," Knapp said.

The reverse often happens in winter, she said. Most furnaces take in cold outdoor air, heat it and thus lower its humidity level. The results then can range from static electricity to dry skin.

Knapp heads the official Kansas Weather Data Library, housed in Manhattan with Kansas State University Research and Extension. The WDL maintains historical and current weather measures and provides a cross-section of station-specific information on the Web site at http://www.oznet.ksu.edu/wdl/.