I live in downstate Illinois away from Lake Michigan. Not sure about Rockford, but my experience is if you live near the lake temperatures can lag about a month behind from downstate locations. I went to boot camp way back in the day at Great Lakes Naval training center and froze my rear end off even at the beginning of May..
We don’t get lake effect winds or snow here, I just remember from my youth we were already enjoying the outdoors a lot earlier than we do now.