SPRINGFIELD, IL – October temperatures were 3.8°F below normal and the 9th coldest October on record. Temperatures across the state dropped to the freezing mark or lower for the first time this fall on October 12 and 13, including a low of 20oF at Park Forest on October 12. Those temperatures effectively ended the 2006 growing season. As a result of the cold weather, October heating degree days (HDDs), a measure of home heating demand, were 38 percent above normal and averaged 462 HDDs statewide compared to the normal 335 HDDs.
Preliminary data for Illinois indicate that October’s 3.97 inches of rainfall was 1.05 inches above normal. “Rainfall has been much above normal in southern, central, and northeastern Illinois, especially the Chicago area,” said State Climatologist Jim Angel of the Illinois State Water Survey, a division of the Illinois Department of Natural Resources.
Midway Airport reported 3.80 inches of rain on October 3, the largest one-day rainfall of the month, and the Chicago Botanic Garden reported 7.75 inches, the largest monthly total. The U.S. Drought Monitor depicts the area between Quincy and Moline in western Illinois, where rainfall has been about 25 percent below normal, as being in “moderate” drought, however.
Historically, a colder-than-normal October does not increase the chance for a cold winter. In fact, previous cold Octobers were more likely to be followed by December–February periods with temperatures near normal.
The National Weather Service winter outlook still calls for an increased chance of temperatures above normal across Illinois and precipitation below normal in the southern two-thirds of the state.
Complete climate data can be found at the Illinois State Water Survey’s website: http://www.sws.uiuc.edu