Illinois Weather: Warm Year Ends With Cold, Dry December

2017 was the sixth-warmest year on record in Illinois, with a statewide average temperature of 54.3 degrees, or 2 degrees above normal, in spite of the extremely cold ending to December.

Eight of the 12 months in 2017 brought above-normal temperatures, according to Illinois State Climatologist Jim Angel of the Illinois State Water Survey, part of the Prairie Research Institute at Illinois. The state experienced the warmest February on record with a statewide average of 41 degrees, 10.1 degrees above normal.

On the other hand, Illinois’ 10th-coolest August on record came in 2017, with a temperature of 70.5 degrees, 3.1 degrees below normal.

The statewide average precipitation for the year was 37.65 inches, 2.31 inches below normal, despite the dramatic precipitation events that occurred in 2017, such as the heavy rains in southern Illinois in spring, and in northern Illinois in July and September.

Illinois received 6.86 inches of rain in April, 3.08 inches above normal, and the fifth-wettest April on record. Still, Illinois experienced its fifth-driest September on record with only 0.82 inches, 2.41 inches below normal.

Some exceptionally dry areas still exist in central Illinois, around St. Louis, and parts of southeastern Illinois. These will be areas to watch in spring for the 2018 growing season.

Snowfall for the 2017-18 winter season started slowly but finished with some significant accumulations by the end of December. Snowfall totals ranged from 6 to 15 inches in the northern half of the state and down to almost zero in far southern Illinois by Dec. 31.

The statewide average precipitation total for December in Illinois was 0.86 inches, 1.83 inches below normal and the eighth-driest December on record. Far southern Illinois received 1 to 3 inches of precipitation, but the rest of the state received less than an inch.

December temperatures in Illinois were exceptionally mild until Christmas Eve. The cold and warm weather balanced out in December, leaving the statewide average temperature for the month at 28.9 degrees, 1 degree below normal.

The largest snowfall totals stretched from the Quad Cities and passed just south of Chicagoland. Cissna Park in Iroquois County reported the largest winter snowfall total of 15.5 inches. Overall, the state remained below normal on December snowfall.

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