CHAMPAIGN — September was the first cooler and wetter than normal month in 2012, according to Illinois State Climatologist Jim Angel of the Illinois State Water Survey at the University of Illinois in Urbana-Champaign.
The statewide average temperature for September in Illinois was 64.6 degrees, 1.6 degrees cooler than normal. This was the first cooler than normal month of 2012, and the first cooler than normal month since September of 2011.
The statewide average precipitation for September was 4.9 inches, 1.7 inches wetter than normal. This is the first wetter than normal month in 2012.
Much of the September rainfall came from the remains of Hurricane Isaac that passed over Illinois on Labor Day weekend. Additional rains fell later, especially in south-central Illinois. In general, areas south of Interstate 80 had monthly totals in the 3- to 12-inch range. A few sites in that region reported over 1 foot of rain with the largest total at Centralia with 15.89 inches.
Precipitation totals north of Interstate 80 were around 1 to 2 inches. One of the driest spots in the state was Elburn (Kane County IL-KN-30) with only 1.28 inches for the month. Chicago and Rockford were not far behind with O’Hare Airport reporting 1.76 inches, while the Rockford airport reported only 1.74 inches for September.
By the end of September, drought conditions had eased somewhat, according to the U.S. Drought Monitor. Only 6.7 percent of the state was in the worst two categories of drought (D3 and D4). This compares to 70 percent of the state in the two worst categories at the end of August. Even so, 82 percent of the state still remained in some stage of drought at the end of September.
Remarkably, the precipitation over the past two months has erased the precipitation deficit since January 1 in much of Fayette, Washington, Clinton, Bond, and Montgomery counties. Sizable deficits of 8 to 16 inches remain across much of Illinois, especially western and northern Illinois as well as far southern Illinois.
Even with a wet September, the January-September precipitation total of 22.38 inches was 8.34 inches below normal and the fifth driest on record.
The January-September average temperature of 59.6 degrees was 4.1 degrees above normal. It was the second warmest January-September on record and just slightly cooler than the record of 59.7 degrees set in 1921.
The Illinois State Water Survey at the University of Illinois at Urbana-Champaign, a division of the Prairie Research Institute, is the primary agency in Illinois concerned with water and atmospheric resources.