October 22nd was the last day on which Chicago received more than a half inch of rain. Data from O'Hare International Airport also posts a rainfall deficit of 10.63 inches for the year. As of December 11th, much of the region remained in moderate to severe drought. Low pressure approaching from the central Plains promises to erase some of this rain shortage. Ample Gulf of Mexico moisture will be drawn into this system, bringing most of northeast Illinois around a half inch of rainfall Saturday and Saturday evening.
Satellite imagery suggests a change to a colder, wetter weather pattern may be underway. A series of disturbances across the north Pacific are expected to move across the U.S. and develop a deep trough over eastern North America. This type of pattern typically brings polar air across the Midwest.