The high temperatures at O'Hare the last three days have been
21°C, all of them very close to the normal temperatures for mid-May. Right now it's 21°C, and forecasters expect record temperatures today and tomorrow (with a brief interlude tomorrow afternoon as temperatures plummet 11°C for a few hours).
The record high for March 14th is 25°C, set in 1995, during Chicago's longest string of 21°C-plus temperatures in history (5 days, from March 12 to 16). With a forecast (record!) high of 27°C tomorrow (beating the record of 23°C, also set in 1995), it's more like June than March.
Not to beat the drum or anything, but warm springs usually lead to really hot summers. Expect whinging from The Daily Parker in about two months.