First Half of September in Illinois – Warmer than Average

The first half of September in Illinois was warmer than average, about 3.5 degrees above average.


Precipitation for the first half of September is mixed. A few areas east of St. Louis and along the eastern border with Indiana have seen 3 to 4 inches, which is well above average. Much of the rest of the state has seen a respectable 1 to 3 inches. Western Illinois has been drier.


Hot, Dry Start to September in Illinois

Illinois and the rest of the Midwest are off to a hot start in September. As the map below shows, areas in shades of brown were up to 9 degrees above average. This includes southern Illinois and much of the southern states in the Midwest. The areas in pinks and red were even farther above average, some 9 to 12 degrees above average. This includes most of the northern half of Illinois, as well as northern Missouri, Iowa, Minnesota, Wisconsin, and most of Michigan.

Cooler and more seasonable weather is expected in Illinois after today.


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September Was Cool and Wet for Illinois


September was 1.5 degrees cooler than average and 0.88 inches wetter than average for Illinois. Year to date temperatures were 3.3 degrees below average and the 6th coolest January-September on record. The year to date precipitation was 32.91 inches, 2.5 inches above average.


The statewide average temperature for September in Illinois was 64.4 degrees, 1.5 degrees below the 1981-2010 average.

The statewide average precipitation for September in Illinois was 4.12 inches, 0.88 inches above average. The heaviest rains fell across western and central Illinois with amounts of 6 to 9 inches (map below). A second area of heavy rains occurred south of Interstate 70 near Effingham. The largest monthly total reported so far is Beardstown with 10.72 inches.


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Summer Weather Gives Way to Fall

If you look at the start to September, temperatures have run 3 degrees above average. And yesterday and today have been the hottest yet with temperatures the 80s and 90s across much of state. But that is about to change as a cold front pushes through later today. This weekend and next week will be cooler with highs in the 70s and low 80s.  I am looking forward to that.

Average daily highs in September in Illinois range from the low to mid 70s in northern Illinois to the low 80s in southern Illinois (map below, click to enlarge).


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