September in Illinois: cooler and wetter than normal

[October 05, 2012]  CHAMPAIGN -- September was the first month this year that was cooler and wetter than normal, according to Jim Angel, Illinois state climatologist, 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. It was the first cooler-than-normal month this year and the first cooler-than-normal month since September last year.

The statewide average precipitation for September was 4.9 inches, 1.7 inches wetter than normal. It was the first wetter-than-normal month this year.

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, in Kane County, 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 with 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 last two months has erased the precipitation deficit since Jan. 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.

[Text from file received from the Illinois State Water Survey]