Chicago — A layer of frost has gripped the city of Chicago and it's not letting go. The Chicago River looks more like the Chicago ice rink, putting the fire department's ice breaker into overdrive.

It's shattering the ice to deter people from walking on it, and so emergency boats can pass.

"It was hard to get the mast down to start and get the motors working," said Lt. Jay Tetrev. The boat was rumbling beneath the ice. "You don't realize it but its riding on top of the ice breaking," he said.

It was negative 10 degrees on board, a warm up from Thursday morning's record-breaking negative 21 in Chicago.

In Saint Paul, Minnesota, the low hit negative 24. That's where CBS News' DeMarco Morgan found dozens huddled in a train station-turned-warming center, including Steven Hicks who's homeless and has frostbite.

"Right now all the shelters are full, people have nowhere else to go. Now whoever is outside is probably going to be outside," he said.

Outside in the deadly deep freeze, that's claimed more than a dozen lives since Sunday, including an 18-year-year University of Iowa student found dead on campus.

Most of the Midwest will warm slightly as the polar air moves east toward New York City, where wind chills plunged below zero. In upstate New York the upper level of Niagara Falls is covered in ice, where rushing water is resisting the freeze, for now.

In Chicago, first responders have gotten calls almost every day this week about people in duress on the ice. Chicago is supposed to enter positive temperature territory on Thursday. But not before a little more snow