The preliminary statewide average May temperature was 66.7 degrees, 3.5 degrees above the 1991-2020 average and the 11th warmest on record going back to 1895. The preliminary statewide average total May precipitation was 4.85 inches, 0.08 inches above the 1991-2020 average and the 42nd wettest on record statewide.
Data are provisional and may change slightly over time
January to April this year was the fourth warmest start to any year on record in Illinois, with only 1921, 2012, and 2017 surpassing 2024. May continued the warm pattern across the state. Daily average temperature and departures from normal in Cahokia Heights show nearly all days last month were warmer than normal, some of which between 10 and 12 degrees above normal (Figure 1). That said, Illinois largely escaped early season extreme heat that we experienced in 2021 and 2022, making for largely pleasant temperatures last month.
May average temperatures ranged from the high 50s in northern Illinois to the low 70s in southern Illinois, between 2 and 4 degrees above normal (Figure 2). Several stations saw their first 90-degree temperatures last month, including 91 degrees in Monmouth and at Chicago’s Midway Airport. Meanwhile, the state was largely spared a late spring freeze in May, with only a handful of stations experiencing temperatures below 40 degrees. Overall, the warmest place in the state last month was Du Quoin, with an average temperature of 72.5 degrees, and the coldest place in the state was Mundelein with an average temperature of 59.2 degrees. Last month was the 7th warmest May on record in the St. Louis area and in Quincy, the 10th warmest May on record in Carbondale, and 11th warmest May on record in Peoria.
Overall, the preliminary statewide average May temperature was 66.7 degrees, 3.5 degrees above the 1991-2020 average and the 11th warmest on record going back to 1895.
May capped off a very warm climatological spring season. Each of the three spring months brought average temperatures that were 2 to 6 degrees above normal (Figure 3). It was a top five warmest spring on record throughout virtually the entire state, including the 3rd warmest on record in Chicago and the 2nd warmest on record in Peoria. For perspective, the spring 2024 average temperature in Peoria of 56.9 degrees is a full 2 degrees less than spring 2012, illustrating just how incredibly warm spring 2012 was. Overall, the preliminary average climatological spring temperature in Illinois was 55.6 degrees which, if confirmed, would tie 2024 for the fourth warmest spring on record statewide. Only 1977, 1991, and 2012 featured warmer springs in the prairie state.
A Mixed Bag of May Precipitation
May is the third wettest month climatologically in Illinois, and the wettest in parts of southern Illinois. However, last month was variable across Illinois, with extremely wet conditions in far southern Illinois and near to slightly drier than normal conditions in central and northern Illinois. Specifically, total May precipitation ranged from around 3.5 inches in west-central Illinois to nearly 10 inches in parts of southeast Illinois. Most areas south of Interstate 64 were 1 to 4 inches wetter than normal last month, while areas farther north were near to 1-2 inches drier than normal (Figure 4).
Unfortunately, much of last month’s precipitation came from thunderstorms that also brought severe weather to Illinois. The NOAA Storm Prediction Center listed 24 tornado reports, 153 severe wind reports, and 56 severe hail reports in Illinois in May. Among these include an EF-3 tornado that tore through parts of Jackson and Williamson Counties, causing significant damage around the Lake of Egypt area.
Climatological spring was wetter than normal for the entire state, with totals ranging from around 12 inches in central Illinois to nearly 18 inches in far southern Illinois. Most of the state was 1 to 4 inches wetter than normal this spring (Figure 5).
June & Summer Outlooks
June is the start of climatological summer and is an exciting month for many reasons. Warm weather is here, schools are out, and cicadas are buzzing (even more than usual this year). Unfortunately, the Climate Prediction Center’s June outlook is less exciting than the month’s weather. The one-month outlook is decidedly undecided in Illinois, with equal chances of warmer, cooler, drier, and wetter weather.
The summer season outlooks (June through August) are a bit more insightful, with higher chances of above normal temperatures this summer. For precipitation, Illinois is squeezed between a band of expected drier than normal conditions to the west and wetter conditions to the east. That setup often, but not always, corresponds with active stormy weather in the summer.
