Dew Point Temperature Overview |
Dew PointBecause 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) |