Ah, Spring in Chicago, when the wind shifts ever so slightly to make you wish you'd layered better:
WGN's Tom Skilling explains what happened:
Temps down more than 16°C from Sunday’s levels Monday, largely the product of winds off the 9°C lake waters—warming returns over coming week with temps surging from 21°C Tuesday to 25°C Wednesday, 27°C Thursday and 26°C Friday but expect easterly lake breezes to cool immediate lakeshore areas each day this week. Weather dries and mixed sun appears Tuesday with lots of sun Wednesday, but wet weather returns with gulf moisture late week and this weekend.
The southbound pneumonia front which induced Sunday afternoon and evening’s sharp pullback ignited explosive t-storm development mainly south of Chicago late Sunday into Sunday night. These storm’s lightning displays and hail production were impressive with some stunning rainfalls—like the 92 mm which fell at Grant Park in Kankakee County and the 82 mm in Will county’s Wilmington. Other impressive totals include 81 mm at Mendota, 71 mm at Carbon Hill and 62 mm at Channahon. But, while those rains were impressive, only 4 mm were reported at O’Hare and 3 mm at Midway Sunday into Monday.
It's unusual for me to go from A/C to heat in one day, but again, this is Chicago in May.