Pedestrians walk along Michigan Avenue in Chicago this week. Bitter cold is hitting much of the Northern half of the U.S., with temperatures dipping into the single digits and below zero. The extremely frigid weather is expected to last for days.

Pedestrians walk along Michigan Avenue in Chicago this week. Bitter cold is hitting much of the Northern half of the U.S., with temperatures dipping into the single digits and below zero. The extremely frigid weather is expected to last for days.