The statewide average temperature for May in Illinois was 70.6 degrees, 7.9 degrees above normal and the warmest May on record, according to Illinois State Climatologist Jim Angel at the Illinois State Water Survey, part of the Prairie Research Institute at Illinois. The old record was 69.4 degrees in 1962.
Daily records indicate that Springfield, Champaign, Quincy and Carbondale all had daily mean temperatures at or above normal for each day of the month. On the other hand, Chicago, Rockford and Peoria had a few dips into the below-normal territory, but average temperatures in these cities finished above normal for the month.
The statewide average precipitation for Illinois in May was 3.98 inches, 0.62 inches below normal. Areas in northern and southwestern Illinois received sizable rainfall amounts.
Meanwhile, precipitation amounts in a few spots in east-central and southeastern Illinois were well below normal and a cause for concern as the summer begins. The highest monthly total reported in the state was at Barrington in Cook County with 12.69 inches. On the other hand, Effingham reported one of the lower totals in the state with 1.11 inches.
One of the key rainfall-producing systems in Illinois in May was when the remains of the subtropical storm Alberto tracked up the Illinois-Indiana border. The remains of tropical storms have reached Illinois in the past.
The National Weather Service’s Climate Prediction Center released its updated outlook for June. In Illinois, there is a greater chance of seeing the above-normal temperatures continue in June. The area around Chicago has an increased chance of below-normal rainfall, which may be welcome after the wet May. Forecasts show Illinois has an increased chance of both warmer and drier than normal conditions for the first half of June.