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A change in the weather

September cooler, wetter than normal

Published: Wednesday, Oct. 10, 2012 4:59 a.m. CDT

CHAMPAIGN, Ill. — 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, in fact, the first cooler-than-normal month since September of 2011.

In Grundy County, according to the Weather Data Division of the county Emergency Management Agency, the average September temperature here was 64 degrees, even cooler than the statewide average.

The high-mercury mark for the month was 94 degrees on Sept. 4, while the low point was 35 degrees on Sept. 24. The temperature hit 90 or better on only one other day during the month.

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, 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, and the Rockford airport reporting only 1.74 inches for September.

Rainfall in Grundy County was also on the low end of the scale, with just 2.03 inches recorded by EMA. More than a quarter of that total, .56 inches, came on Labor Day weekend, during the 24 hours preceding 8 a.m. on Sept. 2. Rain fell a total of 10 times during the month.

The two inches of rain that fell in September raised the liquid precipitation total for the year at Morris to 18.64 inches.

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 last 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.

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