The preliminary statewide average April temperature was 53.1 degrees, 0.5 degrees above the 1991-2020 average and tied for 42nd warmest on record going back to 1895. The preliminary statewide average total April precipitation was 5.46 inches, 1.22 inches above the 1991-2020 average and 18th wettest on record statewide.
Data are provisional and may change slightly over time.
Summer or Winter? Why not Both?
April is a transition month in Illinois, moving us from winter to summer. As with most years, last month gave us a taste of all seasons. Daily average temperatures and departures from normal in DeKalb show the ups and downs typical of April temperatures (Figure 1). The daily average temperature in DeKalb went from 35 degrees on April 9 to 69 degrees on April 29.
April average temperatures ranged from the high 40s in northern Illinois to the high 50s in southern Illinois, between 1 and 3 degrees above normal (Figure 2). The short periods of warmer weather in April broke seven daily high maximum temperature records and three daily high minimum temperature records. Meanwhile, the colder weather in the first half of the month broke three daily low maximum temperature records and two daily low minimum temperature records. Waukegan was the coldest place in the state last month with an average temperature of 46.7 degrees. Carbondale was the warmest with an average temperature of 60.3 degrees.
Overall, the preliminary statewide average April temperature was 53.1 degrees, 0.5 degrees above the 1991-2020 average and tied for 42nd warmest on record.
April Showers
April this year brought a very active storm track and multiple rounds of heavy precipitation, especially in southern Illinois. April total precipitation ranged from around 2.5 inches in northwest Illinois to over 15 inches in southern Illinois. Most of central and northern Illinois were within 1 inch of normal precipitation last month, apart from areas round the Wisconsin border, which were closer to 2 inches drier than normal. Meanwhile, virtually all places south of I-70 were 4 to 8 inches wetter than normal in April (Figure 3).
Among active April weather was an exceptionally intense rainfall event in the first week of the month that produced 6-10 inches of rain in just four days. The event caused moderate to major flooding on many streams and rivers in southern Illinois, and dangerous flash flooding in several places, including in Salem. Figure 4 shows the maximum three-hour, 12-hour, and 72-hour precipitation totals that occurred between April 3 and April 8. The figures also show the estimated return interval of these heavy rainfall totals according to the Illinois State Water Survey’s Bulletin 75 report. While maximum rainfall totals at shorter intervals like one or three hours were intense, they were maximally a 10-year return interval, or a 10% annual exceedance probability. However, the longer duration totals had much higher return intervals. The 72-hour totals, exceeding 10 inches in some places, had estimated return intervals between 25 years and 500 years across most of southern Illinois, indicating truly extreme rainfall had occurred.
Last month was the wettest April on record in St. Louis and Fairfield and was a top 10 wettest April on record for most places in southern Illinois. Overall, the preliminary statewide average total April precipitation was 5.46 inches, 1.22 inches above the 1991-2020 average and 18th wettest on record statewide.
Very Limited April Snow (You’re Welcome)
The first 80-degree day in many parts of Illinois is on par with any of the great weather gifts we have, like a Christmas morning snow or an October afternoon with winds below 20 mph. But if you’ve lived in Illinois for more than a year, you should be weary of the snow that inevitably follows that first taste of summer temperatures. This year, though, no measurable snow came to Illinois in April. Many stations in central and northern Illinois recorded trace snowfall in the first week of the month, but no accumulation.
Given the rarity of May snow in Illinois, I am confident in my proclamation of the end of the 2024-25 snowfall season. Snowfall totals in Illinois ranged from around 3 inches in far southern Illinois to nearly 25 inches in parts of southeast Illinois. An active winter stormtrack across the Interstate 70 corridor in January and February kept south-central Illinois 1 to 10 inches snowier than normal. Meanwhile, most of central and northern Illinois had between 3 and 25 inches below normal snowfall, with the largest negative departures in northeast Illinois (Figure 5).
Outlooks
Even though April can give us a taste of summer, May is the first month where we really experience summer weather. May outlooks from the Climate Prediction Center show highest chances warmer and drier than normal weather this month in Illinois (Figure 6).
May is the month where we start to get a better picture of what summer may bring in Illinois. The most recent summer (June through August) outlooks from the Climate Prediction Center show continued best chances for warmer than normal weather, with slightly higher chances of below normal precipitation in western Illinois (Figure 7).
