April breaks weather records
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.
Figures in the full blog 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. However, the longer duration totals had much higher return intervals, and the 72-hour totals represented truly extreme precipitation. Rainfall, exceeding 10 inches in some places, had estimated return intervals between 25 years and 500 years across most of southern Illinois.
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.
Total precipitation ranged from around 2.5 inches in northwest Illinois to more than 15 inches in southern Illinois. South of I-70 ran 4 to 8 inches wetter than normal in April. Most of central and northern Illinois were within 1 inch of normal precipitation last month, apart from areas around the Wisconsin border, which were closer to 2 inches drier than normal.
No measurable snow fell in Illinois in April. Many stations in central and northern Illinois recorded trace snowfall in the first week of the month without accumulation.
Overall, the preliminary statewide average total April precipitation was 5.46 inches, 1.22 inches above the 1991-2020 average and the 18th wettest on record statewide. 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.
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. 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.
Outlooks
Even though April can give a taste of summer, May is the first month to offer real summer weather. May outlooks from the Climate Prediction Center show the highest chances of warmer and drier than normal weather this month 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.
Data are provisional and may change slightly over time.
For more information about monthly Illinois weather summaries, current conditions, and climate, visit the Illinois State Climatologist website.
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