Bitterly cold temperatures will be the main weather story through midweek as an arctic air mass settles over the region. Wednesday night and Thursday night will be the coldest nights this week, and wind chills will drop well below zero during this time frame. As is typical at night, the city of Chicago will stay warmer than most outlying locations. Relatively warmer temperatures will start to move back in by the end of the week as low pressure develops to our west, and precipitation chances will also increase as the low approaches. While snowfall is initially expected on Friday, temperatures will begin to warm enough from the south that we could see a wintry mix in some locations Friday night into Saturday.