Dew Point Temperature Overview

Dew Point

Because Dew Point temperature is conceptually abstract and difficult to measure, it is not usually mentioned in television weather reports. This is unfortunate, since Dew Point temperature is substantially more useful in depicting the comfort effects of atmospheric water content than is Relative Humidity. Dew Point temperature is defined as the temperature air would have to be cooled to in order for saturation to occur.

Unlike relative humidity (which almost always falls as air temperature increases), Dew Point temperature tends to show modest fluctuation throughout the day, typically varying by a few degrees.  Dew Point temperature tends to be an accurate predictor of human comfort. It makes sense to say, "It's not the heat, it's the Dew Point."

"Studies by Koch et al. in 1960 demonstrated that Dew Point temperatures in still air had a negligible effect on comfort until the Dew Point temperature reached 50°F and the ambient temperature reached 65°F. Below these temperatures, ambient temperature alone was the governing factor." (J.L. Kennedy, Ask Analytic Services.)

"Generally, when the Dew Point temperatures reaches 60 degrees, most people will start to notice the air beginning to feel humid. At 65 degrees, it starts to feel uncomfortable and as it climbs close to 70 degrees it becomes very noticeable. Dew Point temperatures over 70 degrees feel downright oppressive." (NWS Grand Rapids, MI)

 "The Dew Point is the temperature to which air must be cooled to reach saturation. Dew Point temperatures are an excellent measure of the amount of water vapor in the air. Dew Point temperatures in the 70's are considered tropical and Dew Points greater than 80 degrees are extremely rare. At 1100 AM on July 30, 1999,  the Dew Point temperature at the Twin Cities International Airport reached 81 degrees. This is the highest Dew Point temperature ever recorded in the Twin Cities. The previous record was 80 degrees, recorded as recently as July 22, 1999. The high Dew Point temperatures, in conjunction with sweltering air temperatures in the mid to upper 90's, combined to produce heat index values exceeding 110 degrees in many southern Minnesota communities." (climate.umn.edu)