In St. Louis, where temperatures were expected to stay below freezing for at least a week, additional shelter beds were made available for the homeless. Mayor Joe Hogsett of Indianapolis warned of “extreme cold” in his city and offered tips on identifying frostbite and hypothermia. And in New York, a “Code Blue” was declared for the city’s homeless, guaranteeing them overnight shelter.

“We strongly encourage all New Yorkers to stay inside as much as possible during this week as the cold weather continues,” Mayor Bill de Blasio wrote Wednesday on Twitter. “Check on neighbors when you can and bring your pets inside.”

For North Dakota, Wednesday was something of a reprieve.

“Actually, today we’re up to positive six,” said Zack Hargrove, a meteorologist with the National Weather Service in Bismarck. “That’s nice. The last two days, we didn’t get above zero.”

The cold weather was not expected to relent soon. Mr. Hargrove said weekend highs in Bismarck could be around minus 12. In Boston, wind chills overnight Wednesday were expected to reach minus 10. And in Arlington Heights, Ill., the police said they had canceled a drunken-driving checkpoint scheduled for Friday “due to extreme cold.”

The bitter weather was not without redeeming qualities. City crews in Lawrence, Kan., were preparing an ice-skating rink in a park, a tradition that the local newspaper said had melted away in recent warm winters.