September so far in Illinois has been warmer than normal with areas of widespread rain. The statewide average temperature is 72.4 degrees, 1.9 degrees above normal. The statewide average precipitation is 2.03 inches, 0.99 inches above normal.
The rains in September have been widespread across the state with heavier amounts of 3 to 5 inches east of St. Louis and across central Illinois (left panel, blue shading). That is about 1 to 3 inches above normal for the first 12 days of September (right panel, darker green shading). Click to enlarge.
Temperatures in Illinois have been running about 2 degrees above normal for September. The average high temperatures have been running near to slightly above normal (left panel) while the average low temperatures have been running 2 to 4 degrees above normal across much of the state (right panel).
Below are the temperature departures from normal by day for September in Champaign-Urbana, the site located just behind my office. It is typical of the temperature pattern experienced across Illinois with cooler temperatures in the first three days, followed by a rapid transition to warmer temperatures through September 9, with cooler than normal conditions over the weekend.