The preliminary statewide average December temperature was 33.4 degrees, 1.8 degrees below the 1991–2020 average and tied for 36th warmest on record going back to 1895. The preliminary statewide average total December precipitation was 2.90 inches, 0.47 inches above the 1991–2020 average and tied for 31st wettest on record statewide.
Data are provisional and may change slightly over time.
Roller Coaster Temperatures
Day to day temperature variability in Illinois is highest in climatological winter, and December followed suit with regular dips and jumps in daily temperature, as shown in Figure 1 from Aurora. Daily average temperatures were 10 to 20 degrees below normal in the first week of the month, were 15 to 25 degrees above normal in the final week of the month, and jumped around in between (Figure 1).
When taken altogether, December average temperatures ranged from high 20s in northern Illinois to the low 40s in southern Illinois, between 1 and 5 degrees above normal (Figure 2). The warmest place in the state last month was Olmstead in Pulaski County with an average December temperature of 41.4 degrees. The coolest place in the state was Stockton in Jo Daviess County with an average December temperature of 26.6 degrees.
The milder days last month broke 3 daily high maximum temperature records and 54 daily high minimum temperature records. Meanwhile the cooler days in December broke 23 daily low maximum temperature records and 6 daily low minimum temperature records in Illinois.
Overall, the preliminary statewide average December temperature was 33.4 degrees, 1.8 degrees below the 1991–2020 average and tied for 36th warmest on record going back to 1895.
Wetter December with Some Snow, I Guess
December wasn’t a washout anywhere but brought enough precipitation to continue improving water conditions from peak fall drought. December total precipitation ranged from over 6 inches in far southern Illinois to around 1.5 inches in northern Illinois. Most areas of the state south of Interstate 64 were 1 to 3 inches wetter than normal last month, while parts of northern Illinois were around 1 inch drier than normal (Figure 3).
The wettest part of the state was, again, Olmstead in Pulaski County, which picked up just over 10 inches in the final month of the year. The driest place in the state in December was Freeport, with only 0.89 inches for the month. Overall, the preliminary statewide average total December precipitation was 2.90 inches, 0.47 inches above the 1991–2020 average and tied for 31st wettest on record statewide.
As is often the case in milder Decembers, snowfall was a little harder to come by across Illinois last month. December total snowfall ranged from around 5 inches in far northern Illinois to less than a tenth of an inch in far southern Illinois, between 1 and 6 inches below normal (Figure 4). Snowfall so far this season has also been below normal across Illinois, to the tune of 1 to 10 inches.
Outlooks
Climate Prediction Center outlooks for January show an extension of colder than normal conditions from the northern Plains into much of the Midwest and Southeast US. January Outlooks show mostly equal chances of above and below normal precipitation for the first month of 2025 (Figure 5).
Meanwhile, 3-month outlooks for January through March show equal chances of warmer and cooler than normal conditions but paint a decidedly wetter than normal pattern across Illinois (Figure 6).
