How will climate change impact Chicago's rainiest month?

CHICAGO (CBS)-- Following Chicago's heaviest one-day rainfall in seven months, get ready for more muddy backyards in May.

Rounds of rain added up to 1.31" in the gauge at Chicago Midway on Sunday -- the airport's heaviest one-day rainfall since September 2023. Another round of heavy rain fell early Monday morning, leading to three-day rainfall totals of over 3 inches in parts of northeast Illinois. 

Minor flooding is being observed in parts of La Salle County on the Vermillion and Illinois rivers. 

Wednesday kicks off what is typically the Chicago area's stormiest month of the year -- May. Over the last 30 years, a typical May has brought Chicago 4.49" of rain and also the kick-off of our traditional severe weather season which runs through the middle of summer.

Monthly outlooks from the NOAA Climate Prediction Center indicate a typically rainy May in northeast Illinois and northwest Indiana, with odds favoring near-normal rainfall next month. 

As the climate warms, May rainfall is getting heavier in Chicago. 

Data from Chicago O'Hare shows May rainfall has increased by 42% in the last 30 years, from an average of just 3.17" in 1989 to 4.49" in 2020. This is because warmer air holds more moisture.

These trends are consistent with broader trends observed across the Upper Midwest. Data from Climate Central shows annual rainfall has increased by 4-6 inches in Illinois and by even higher amounts in Indiana and Iowa.