September in Illinois – Cool

Based on preliminary numbers, the statewide average temperature for September in Illinois was 63.2 degrees, 3 degrees below average. That makes it the 13th coolest September on record for Illinois. The coolest September was 1918 with 59.3 degrees. Statewide records go back to 1895.

Despite the overall cool readings for the month, Labor Day weekend was very hot. Highs in the upper 90s and low 100s were common during that time. One of the hottest was Quincy with 104 on September 1. In all, at least 65 stations in Illinois either tied or broke daily records for high temperatures in early September (text file with details).

On the other extreme, the coldest spot for the month was Paw Paw with 32 degrees on September 15. Twenty-two stations either set or broke daily records for low temperatures (see text file for details).

The statewide average precipitation for September was 3.53 inches, 0.34 inches above average. Rainfall was stubbornly sparse in the areas hardest hit by drought where only 1-2 inches were common. Amounts in far southern and northern Illinois were much wetter at 4-8 inches.

The highest rainfall total for the month was by a CoCoRaHS observer in Bush, Illinois, with 8.42 inches. In second place was a CoCoRaHS observer in Harrisburg, Illinois, with 8.04 inches. The reported driest spot in the state was a CoCoRaHS observer in Warsaw with only 0.69 inches of rain for the month. CoCoRaHS observers are volunteers that use standard equipment and training. Therefore, their results are comparable to other networks.

September rainfall
September 2011 rainfall for Illinois. Click to enlarge.
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2 thoughts on “September in Illinois – Cool

  1. Hi Jim,
    I came across this blog accidentally whilst browsing others and collecting atmospheric sciences related blogs –to which I quickly added this one. Thanks for the info you provide here!

    Two recent papers I’ve seen specifically concern central Illinois climate so might be worth sharing:

    Westcott et al: Predicting the Seasonal Shift in Mosquito Populations Preceding the Onset of the West Nile Virus in Central Illinois http://journals.ametsoc.org/doi/abs/10.1175/2011BAMS3163.1

    Wang et al: Climate change impact on meteorological, agricultural, and hydrological drought in central Illinois http://www.agu.org/pubs/crossref/2011/2010WR009845.shtml

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