(Image source from: The New York Times)

The temperature plunge in Midwest cities in the United States, officials were prompted to take extraordinary steps to protect the homeless and other vulnerable people from the bitter cold, including turning some city buses into mobile warming shelters in Chicago.

Due to extremely cold temperature, governors in Wisconsin, Michigan, and Illinois declared emergencies as the worst of cold threatened on Wednesday.

The U.S. Postal Service, it will not deliver mail in parts of the Midwest Wednesday because of the cold, which is in the aftermath of a split in the polar vortex that allowed temperatures to dip much further south in North America than average.

The National Weather Service forecast for Wednesday night called for temperatures in Chicago as low as minus 28 (negative 33 degrees Celsius), with wind chills to minus 50 (negative 46 degrees Celsius). Detroit's lookout was for Wednesday overnight lows around minus 15 (negative 26 degrees Celsius), with wind chills falling to minus 40 (negative 40 degrees Celsius).

"These are actually a public health risk and you need to treat it appropriately," Chicago Mayor Rahm Emanuel said Tuesday. "They are life-threatening conditions and temperatures."

A wind chill of minus 25 (negative 32 degrees Celsius) can freeze skin within 15 minutes, according to the National Weather Service.

Due to the weather system, at least four deaths were recorded, including a man struck and killed by a snow plow in the Chicago region, a young couple whose SUV struck another on a snow-clad road in northern Indiana and a Milwaukee man found frostbitten to death in a garage.

Homeless off Streets

Officials in large Midwestern cities including Minneapolis, Milwaukee, Chicago, and Detroit were desperately trying to get the homeless off the streets.

Minneapolis charitable groups that operate warming places and shelters expanded hours and capacity, and ambulance crews handled all outside calls as being potentially life-threatening, according to Hennepin County Emergency Management Director Eric Waage. MetroTransit said it wouldn't remove people from buses if they were riding them simply to stay warm, and weren't being disruptive.

Shelters, churches and city departments in Detroit worked together to help get vulnerable people out of the cold, offering the message to those who refused help that "you're going to freeze or lose a limb," said Terra DeFoe, a senior adviser to Detroit Mayor Mike Duggan.

Hundreds of public schools from North Dakota to Missouri to Michigan canceled classes Tuesday, and some on Wednesday as well. So did several large universities.

Closing schools for an extended stretch is not an easy decision, even though most school districts build potential makeup days into their schedules, said Josh Collins, spokesman for the Minnesota Department of Education.

Typical outdoor activities were even shut. A ski hill in the Minneapolis area said it would close through Wednesday, likewise an ice castle attraction.

The cold weather was even affecting beer deliveries, with a pair of western Wisconsin distributors saying they would pause or suspend shipments for concern that beer would freeze in their trucks.

-Sowmya Sangam