Tag Archives: September

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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September – Warm and Dry in Illinois

Strictly speaking, we are not done with September until the end of today. However, I went ahead and pulled together the September statistics because there is no rain in the forecast. All these statistics are based on data that have come in so far and may change slightly in the coming weeks.


The statewide precipitation for September was 1.87 inches, 1.39 inches below average and the 14th driest September on record. As the first two maps below illustrate, dry conditions were widespread. Only a few spots received 3 or more inches in Illinois, including the Chicago area, far western Illinois, and the southeast corner of the state. Several areas in the state received less than an inch of precipitation.

The second map shows the September data as a percent of average. Several areas had less than 25 percent of average (red). Even the “wet” areas had trouble achieving totals close to the 1981-2010 average. Overall, the precipitation departure for September was 57 percent of average.

This is the 6th driest July-September on record for Illinois with 6.64 inches (4.24 inches below average). Ironically, this came on the heels of the wettest January-June on record for Illinois with 28.96 inches (9.13 inches above average).

This is the third month in a row with below-average precipitation. In July, Illinois received 3.14 inches (0.91 inches below average). In August, Illinois received 1.63 inches (1.37 inches below average).


The statewide temperature for Illinois in September was 68.8 degrees, 2.9 degrees above average. It was warm but not record-setting. The warmest September on record was 1925 with 72.7 degrees.

The above-average September reversed the pattern of the last three months (June, July, and August) which were below-average on temperature.

  • June: 71.4° (0.4° below average)
  • July: 72.9° (2.4° below average)
  • August: 72.5° (1.0° below average)
  • September: 68.8° (2.9° above average)

Statewide records began in 1895.