Illinois State Water Survey - University of Illinois at Urbana-Champaign
State Climatologist Office for Illinois
Average Dewpoint Temperatures in Illinois
Dr. Jim Angel, State Climatologist
The dewpoint temperature is one useful way of expressing humidity; it is the point at which air must be cooled before dew will start to form. The dewpoint temperature is a much better measure of humidity than relative humidity. Relative humidity can change when either the moisture content or air temperature changes. In face, average relative humidity for any location for any month in Illinois is about 75 percent. Dewpoint temperatures do not suffer from this problem, and the higher dewpoint temperatures always mean more moisture.
Maps
Maps of annual, winter, spring, summer, and fall dewpoint temperatures (F) in Illinois, based on data from 1991-2000. Click on a figure to enlarge.
