Chicago's temperature dropped below freezing last Wednesday morning and has stayed there since. It's -13°C now, the coldest it's been during this period.
Fortunately some warmer, wetter air is pushing in from the south, and should arrive after midnight. The forecast calls for sustained 9°C temperatures (and non-stop rain) from Saturday morning through Monday afternoon, when another cool air mass will slide into the region and freeze us out again.
Welcome to winter in Chicago. Warm rain and frigid dryness, for three months.