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 of annual, winter, spring, summer, and fall dewpoint temperatures (F) in Illinois, based on data from 1991-2000. Click on a figure to enlarge.

Annual dewpoint temperature for Illinois
Annual Dewpoint Temperature
Winter dewpoint temperature for Illinois
Winter Dewpoint Temperature
Spring dewpoint temperature for Illinois
Spring Dewpoint Temperature
Summer dewpoint temperature for Illinois
Summer Dewpoint Temperature
Autumn dewpoint temperature for Illinois
Autumn Dewpoint Temperature