Video:Trent Ford, Illinois' state climatologist, appears on "Chicago Tonight" on April 17, 2023. (Produced by Eunice Alpasan)

In true springtime-in-Chicago fashion, last week’s record-setting summer-like temperatures gave way to a winter return Monday, as people woke up to snow-covered cars and below-freezing wind chills.

It was a rude awakening for Chicagoans who had basked in last week’s 80-degree heat.

I strenuously object. pic.twitter.com/gHkHzfiE6V

— pantagrapher (@pantagrapher) April 17, 2023

But local hero Dan O’Conor, who's been jumping into Lake Michigan daily since summer 2020, wasn’t bothered by the cold — the water was warmer.

Monday April 17,2023 …

33 Degree Air/ 43 Degree Water Foggy with Snow Flurries …#GreatLakeJumper …

Dedicated to Bob Marley @bobmarley pic.twitter.com/PFNXj045mv

— Great Lake Jumper (@TheRealDtox) April 17, 2023

Last week’s warm temperatures and today’s cold are related, said Illinois State Climatologist Trent Ford. The swing comes from a jet stream, he said. Its ridge brought warm air from the south, which was then followed by a dip in the jet stream that brought cooler air.

“April is the most common time of the year when we do get these big weather shifts, and that’s because areas further to our south are warming up and areas further to our north are still very cold from the winter time so you get kind of those clashes of air,” Ford said.

While day-to-day changes in weather are fairly common this time of year, Ford said the rarity was how persistent the warm weather was last week, making today’s weather seem that much more anomalous.

Ford said it’s looking like the cooler weather will stick around for the rest of April. It won’t be as cold as today, but still below normal temperatures.

Snow-covered cars, April 17, 2023. (Patty Wetli / WTTW News)

Contact Patty Wetli:@pattywetli| (773) 509-5623 |[email protected]