September is a transitional month, characterized by rapidly falling average temperatures. However, following a cooler than normal August, September finished on the other end of the spectrum. Across northern Illinois and Ohio, it was as much as 3 to 4 degrees or more above normal in some locations. In the first week, many locations had the hottest days for the year. In Illinois, Urbana experienced its hottest day of the year September 4th at 93°F while Chicago’s O’Hare Airport tied its hottest day at 92°F on September 6th. Over in Ohio, the hottest day of the year was set at Cincinnati Northern Kentucky Airport with 93°F on September 4th. Akron, Ohio’s normal high temperature for September is below 80 but had seven 90 or higher days. Indianapolis, Indiana reached 90 degrees or higher on seven days; amazingly it did not reach 90 at all in August! Even the lakes had little cooling effect as Cleveland, OH, whose average monthly highs are in the 70’s, had 12 days of 80 or higher.
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Precipitation for the month varied significantly. Northern Illinois experienced a much wetter than normal month with more than 4 inches (125-150% of normal), most of which fell on the 17th & 18th as a strong cold front moved through. In contrast, southern Indiana and southwest Ohio observed rainfall deficits, with some places receiving less than 50% the monthly normal.
The same cold front responsible for the northern Illinois heavy rainfall also led to the most significant severe weather outbreak of the month. On September 18th an EF-1 tornado (86 – 110 mph winds) was observed in Frankfort, Illinois (see the video below for a storm chaser's footage of the supercell), along with several hail and damaging wind reports across northeastern Illinois and northern Indiana. In fact, a strong thunderstorm produced sustained winds of 59 mph in Tippecanoe County, Indiana with gusts estimated to 80 mph!
September also marks the beginning of the corn crop harvesting. The drier conditions across the southern parts of the Midwest allowed for more days of harvesting fieldwork. As of September 20th 83% of the corn crop was mature for harvesting in Kentucky, 78% in Illinois, down to 46% across Ohio. Overall, after a summer featuring below normal temperatures, for both July and August, September swung to the warm side across the Midwest while rainfall was very unevenly distributed.
