chicago

Visitors walk through the holiday lights display "ZooLights" at the Lincoln Park Zoo in Chicago, Illinois...Visitors walk through the holiday lights display "ZooLights" at the Lincoln Park Zoo in Chicago, Illinois

Jim Young/Reuters

Visitors walk through the holiday lights display “ZooLights” at the Lincoln Park Zoo in Chicago, Illinois.

An aerial view at night of the downtown Chicago skyline. An Arctic air mass is expected to chill much of the Central Plains and the East Coast through Monday with wind-chill temperatures dropping into the single digits overnight in some places.

Kiichiro Sato/AP

A nightime aerial view of downtown in the US city of Chicago

Lightning strikes the Willis Tower (formerly Sears Tower) in downtown in Chicago, Illinois. A massive storm system with heavy rain, high winds, hail and possible tornadoes is expected to move into Illinois and much of the central part of the Midwest today.

Scott Olson/Getty Images

Lightning strikes the Willis Tower (formerly Sears Tower) on early Thursday morning in Chicago, Illinois. A massive storm system with heavy rain, high winds, hail and possible tornadoes is expected to move into Illinois and much of the central part of the Midwest.