The clearest statewide peak usually shows up in July. The biggest statewide split is between the South and the North. Carbondale is one of the strongest higher-WBGT examples in the state, while Chicago is a useful contrast. Local city pages are more useful than a single statewide assumption when you are planning around heat.
Illinois tends to have a meaningful midsummer WBGT season without the same persistence seen farther south. July is usually the main stretch to watch most closely. The South tends to run warmer than the North, even though the overall pattern is less persistent than in the South.
In Illinois, the biggest planning value comes from watching the midsummer peak and comparing cities before assuming the whole state behaves the same way. That is usually enough to make this page more useful than a simple statewide average.
Klimo WBGT provides real-time Wet Bulb Globe Temperature monitoring to help athletes, workers and outdoor enthusiasts protect themselves from heat-related illness.
Wet Bulb Globe Temperature (WBGT) is a measure of heat stress that accounts for temperature, humidity, wind speed and sun angle. Rather than relying on the air temperature or the heat index, WBGT captures how the human body actually experiences heat, making it the gold standard for outdoor activity safety decisions.