The preliminary statewide average May temperature was 62.2 degrees, 1.0 degrees below the 1991–2020 normal, 0.1 degrees above the 20th Century average, 1.2 degrees below the most recent 30-year average, and the 62nd warmest May on record.
The preliminary statewide total May precipitation was 2.89 inches, 1.88 inches above the 1991–2020 normal, 1.19 inches below the 20th Century average, 1.82 inches below the most recent 30-year average, and the 33rd driest May on record.
Data are provisional and may change slightly over time
Both March and April were among the top 5 warmest on record statewide in Illinois. However, May slowed our sprint into summer with several days of temperatures that were 5 to 10 degrees below average (Figure 1). Daily temperatures and departures from normal in Galesburg do show a consistent warm-up from early to late month, including above average temperatures in the final week of May.
May average temperatures ranged from the high 50s in northern Illinois to the high 60s in southern Illinois. Most of the state was slightly to somewhat cooler than normal last month, while the northwest corner of the state was around 1 degree warmer than normal (Figure 2). Hot and dry afternoons in the final week of the month broke 4 daily high maximum temperature records and 11 daily high minimum temperature records. Meanwhile, the cooler start to May broke 1 daily low maximum temperature record and 6 daily low minimum temperature records.
Overall, the preliminary statewide average May temperature was 62.2 degrees, 1.0 degrees below the 1991–2020 normal, 0.1 degrees above the 20th Century average, 1.2 degrees below the most recent 30-year average, and the 62nd warmest May on record.
May capped off a very warm climatological spring season. The first month of the season was the 4th warmest March on record statewide, followed by the warmest April on record in Illinois.
March temperatures were 4 to 8 degrees above normal and April temperatures were 1 to 3 degrees above normal (Figure 3). Despite the milder May temperatures, the spring season was still a top 10 warmest on record statewide in Illinois. We had the 3rd warmest spring on record in Springfield, Carbondale, and Champaign-Urbana, the 5th warmest in Peoria and Quincy, 6th warmest record in Chicago, the 7th warmest in Rockford and Moline.
May is climatologically the third wettest month in Illinois, and the wettest month in parts of southern Illinois. While last month’s precipitation was typically variable across Illinois, May was overall drier in most places. Total May precipitation ranged from around 1 inch along the Wisconsin border to over 10 inches in south-central Illinois. The Interstate 70 corridor was near to wetter than normal, while the rest of the state was 1 to 4 inches drier than normal (Figure 4).
Overall, the preliminary statewide total May precipitation was 2.89 inches, 1.88 inches above the 1991–2020 normal, 1.19 inches below the 20th Century average, 1.82 inches below the most recent 30-year average, and the 33rd driest May on record. It was a top 10 driest May on record in Chicago and Peoria, and last month was only the third May on record in Rockford with less than 1 inch of precipitation, after 1992 and 1934. Unsurprisingly, the dry May conditions also produced very little severe weather. Last month brought exactly 1 tornado to Illinois, compared to 70 tornadoes in April.
May dryness was outweighed by exceptionally wet weather in March and April, resulting in a wetter than normal spring season for the northern two-thirds of the state. Spring total precipitation ranged from around 10 inches in eastern Illinois to nearly 20 inches in south-central Illinois.
June is the start of meteorological summer and is an exciting month for many reasons. Warm weather is here and schools are out. The Climate Prediction Center’s June outlook shows best chances of summer starting a bit on the warm side, with best chance of a continued warmer trend for the entire state, and possibly a bit of a drier start to northern Illinois as well as the broader Great Lakes region (Figure 6).
The last Climate Prediction Center summer season (June – August) outlooks show, for the first time in a while, best chances of near normal temperatures this season. The outlooks do not show strong signals either way for precipitation, but do have a dry tendency in the northern Plains (Figure 7).
