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CHAMPAIGN, Ill. — October in Illinois was the eighth warmest and the fourth wettest on record going back to 1895, according to Illinois State Climatologist Trent Ford at the University of Illinois’ Illinois State Water Survey.
Following a warm start to fall in September, temperatures were consistently 5 to 10 degrees above normal for the first half of October. The statewide average October temperature was 59.7 degrees, 5.1 degrees above the 1991-2020 average.
October average daily minimum temperatures ranged from 5 to 9 degrees above normal in Illinois. The average nighttime minimum temperature last month was the highest on record in Chicago, Peoria and Paducah and the top five highest on record in Rockford, the Quad Cities, Quincy and St. Louis.
The highest temperature observed in October was 91 degrees in Congerville in Woodford County, and the lowest temperature was 24 degrees in Galena in Jo Daviess County. The unusually warm weather in October broke 13 daily high maximum temperature records and 58 daily high minimum temperature records.
Precipitation
The preliminary statewide average total October precipitation was 6.36 inches, 3.44 inches above the 1991-2020 average. The persistently wet conditions resulted in monthly totals ranging from 3.5 inches in southwest and far southeast Illinois to over 9 inches in parts of north-central Illinois.
While southern Illinois was between 1 and 3 inches wetter than normal last month, parts of central and northern Illinois were 3 to 6 inches wetter than normal. It was the second wettest October on record in Peoria and Quincy and the fifth wettest in Springfield.
Although the rain put October harvest on hiatus, it was greatly beneficial to improving drought conditions in northern Illinois. Soil moisture and streamflow were both boosted by the wet conditions.
The U.S. Drought Monitor showed improved drought conditions throughout much of northern Illinois in the most recent map. The percentage of the state in at least severe drought declined from 8.78% on Oct. 1 to 1.22%.
Most areas between Whiteside County in northwest Illinois and Lake County in northeast Illinois remain in moderate to severe drought, however, as year-to-date precipitation deficits of 5 to 10 inches remain. Wetter weather will need to prevail throughout winter to terminate the northern Illinois drought, but October was a big step in the right direction.
Outlooks
The outlooks for the whole month of November show equal chances of above and below normal temperatures and precipitation across the state. Following a typical La Niña pattern, the outlook for December-February shows the highest odds of a warmer and wetter than normal winter across the state.