Global warming does this, don’t ‘cha know. </sarcasm>
Chicago had a new all-time record of -31F (-35C) at Chicago Rockford. I know the previous record for Chicago was -27F (-32.8C) in 1985.
“The lowest temperature at Rockford was -31F observed at Chicago Rockford International Airport on January 31st.”
January 30-31, 2019: Record to Near-Record Cold in Northern Illinois
The coldest temperature in Chicago in 34 years (-23°) was recorded on the morning of January 30, 2019 during a bitter cold couple of days. Rockford, IL broke their all-time record cold temperature with a low of -31° on January 31.