September temperatures were - get this - below average

CHAMPAIGN — After 11 consecutive months of above-average temperatures — some months as much as 15 degrees above normal — Champaign-Urbana had a below-normal September.

The mean temperature locally was 65 degrees, 1.2 degrees below normal, according to the Illinois State Water Survey. The average high was 2.4 degrees below normal; the average low was 0.4 degrees below normal.

After an unusually hot summer of eight days of 100 degrees or more, and 55 days of 90 degrees or more, there was just one 90-degree day in September and only seven with readings of 80 degrees or more.

The coldest temperature was 35 degrees on Sept. 24.

The last time the monthly average temperature was below normal was in September 2011, when the mean temperature was 1.8 degrees below normal.

"I think there are a couple of things at work in the last few weeks to change our situation," said state climatologist Jim Angel of the Illinois State Water Survey in Champaign. "Beginning in early August, the ridge of high pressure that had contributed to our earlier drought and heat shifted westward out of the Midwest. This allowed cooler temperatures and more rain-producing weather systems to move through Illinois.

"Another was that we had the remains of Hurricane Isaac that dropped 2 to 5 inches of rain across central and southern Illinois."

Champaign-Urbana precipitation was above normal in September — only the third time that's happened this year, according to the water survey. There was 5.71 inches of rain last month, more than 2 1/2 inches greater than the September average. It rained on 12 of 30 days last month.

It was the 15th wettest September on record, according to Angel.

"As a result," he said, "we have seen a nice recovery in soil moisture and we aren't nearly as far behind on rainfall as we were in July."

At the end of July, Champaign-Urbana was 10.06 inches below average for the year. Now, however, total precipitation for the year is 25.86 inches, 5.85 inches below normal.

Despite September's below-average temperatures, the mean temperature for the year to date is 59.9 degrees, almost 5 full degree above normal.

The 90-day outlook by the National Weather Service says there is a very good chance that temperatures in Champaign-Urbana will be average or above for the remainder of the year. There is a 43 percent chance of above average temperatures, a 33 percent of near normal temperatures and only a 24 percent chance of below average readings. Precipitation is forecast to be near normal.

Average and actual mean temperatures by month, September 2011-September 2012

Month  Mean  Average mean  Difference
September  2011 64.4 66.2 -1.8
October 2011 55.6 53.9 1.7
November 2011 45.7 41.3 4.4
December 2011 35.7 28.9 6.8
January 2012 31.7 24.8 6.9
February 2012 34.8 29 5.8
March 2012 55 40 15
April 2012 54.4 51.9 2.5
May 2012 68.6 62.5 6.1
June 2012 72.5 72.2 0.3
July 2012 82.5 74.9 7.6
August 2012 74.4 73.4 1
September 2012 65 66.2 -1.2

Source: Illinois State Water Survey

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