The warmest September on record was 1933 with 72.2 degrees.
The statewide average precipitation was 3.42 inches, 0.19 inches
above average. However, the precipitation was unevenly
distributed around the state. Most of the state received between
3 to 5 inches, while western and far southern Illinois were much
drier with less than 3 inches of precipitation.
Some of the most sizable monthly precipitation totals were
reported in Vermillion County, near Hoopeston, with one station
reporting 11.78 inches and another reporting 11.74 inches. The
next largest amount in the state was 8.45 inches at the DuPage
County airport.
[Lisa Sheppard, Illinois State Water
Survey]
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