A deep freeze is setting in across the Midwest with low temperatures forecast in the single digits and a few below zero, turning the season’s first major snow into ice that made some roads treacherous to travel.

After snow on Friday and Saturday across much of the region, temperatures plunged behind the front on Sunday. The National Weather Service forecast 20 degrees or lower across six states from North Dakota to Illinois. Fargo, North Dakota could dip to 11 degrees by early Sunday. Madison, Wisconsin could see 7 degrees, Des Moines 12 and Chicago 9.

Parts of Iowa, northwest Illinois and southern Wisconsin could reach zero or below, the weather service said.