U.S. POSTAL SERVICE mail carrier Steve Schaut of Aurora, Wis., bundled up to try and stay warm Tuesday afternoon as he made his rounds on West B Street in Iron Mountain. Home delivery of mail was cancelled today due to the extreme cold. (Theresa Proudfit/Daily News photo)

IRON MOUNTAIN — Dangerous cold conditions today triggered widespread closures of schools along with some businesses and government offices and even prompted the U.S. Postal Service to suspend delivery.

Citing concerns for the safety of employees, the USPS suspended delivery across much of the Midwest, along with western Pennsylvania, the Dakotas and Nebraska. Governors in Wisconsin and Michigan and Illinois have declared emergencies.

Iron Mountain dipped to minus 17 overnight, according to the water treatment plant in Kingsford.

Temperatures in the Iron Mountain area were expected to remain below zero all day, with wind chills reaching 35 below. Tonight’s lows could dip into the minus 20s, with wind chills to 40 below, the National Weather Service said.

A wind chill warning is in effect until 11 a.m. Thursday. The predicted high on Thursday is zero, with a low of about minus 15.

Temperatures should climb into the teens on Friday and soar past 30 on Saturday.

Although mail delivery was suspended today, the postal service was maintaining regular lobby services.

Michigan Secretary of State offices in the Upper Peninsula will be closed until Friday. Social Security offices in the Upper Peninsula were closed today.

All area schools and senior citizen centers were closed today, and the Florence and Goodman-Armstrong Creek school districts in Wisconsin were the first locally to announce Thursday closures.

Across the Midwest, many normal activities shut down and residents huddled inside as the National Weather Service forecast plunging temperatures from one of the coldest air masses in years. The bitter cold is the result of a split in the polar vortex that allowed temperatures to drop much farther south than normal.

In Chicago, temperatures were still dropping after plunging early today to minus 19 degrees, breaking the day’s previous record low set in 1966. Snowplows were idled overnight in southwestern Minnesota, where temperatures dropped to negative 29 degrees. And the temperature in Fargo, North Dakota, was 31 degrees below zero.

In addition to the flight cancelations in Chicago at O’Hare International Airport and Midway International Airport, the extreme cold prompted Amtrak to cancel all trains into and out of Chicago.

Officials throughout the region were focused on protecting vulnerable people from the cold, including the homeless, seniors and those living in substandard housing. Some buses were turned into mobile warming shelters to help the homeless in Chicago.

In Chicago, major attractions closed because of the bitter cold, including the Lincoln Park Zoo, the Art Institute and the Field Museum.

“These (conditions) 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 can freeze skin within 15 minutes, according to the National Weather Service.

In Michigan, homeless shelters in Lansing were becoming “overloaded,” Mayor Andy Schor said. They also were filling up in Detroit.

“People don’t want to be out there right now,” said Brennan Ellis, 53, who is staying at the Detroit Rescue Mission Ministries.

Detroit’s outlook was for Wednesday overnight lows around minus 12, with wind chills dropping to minus 35.

At least four deaths were linked to the weather system Tuesday, including a man struck and killed by a snow plow in the Chicago area, a young couple whose SUV struck another on a snowy road in northern Indiana and a Milwaukee man found frozen to death in a garage.

Hawaii native Charles Henry, 54, was staying at a shelter in St. Paul, Minnesota, and said he was grateful to have a place to stay out of the cold.

“That wind chill out there is not even a joke,” he said. “I feel sorry for anybody that has to stay outside.”

Chicago was turning five buses into makeshift warming centers moving around the city, some with nurses aboard, to encourage the homeless to come in from the cold.

“We’re bringing the warming shelters to them, so they can stay near all of their stuff and still warm up,” said Cristina Villarreal, spokeswoman for the city’s Department of Family and Support Services.

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 and several large universities from North Dakota to Pennsylvania canceled classes Tuesday or planned to do so Wednesday.

American Indian tribes in the Upper Midwest were doing what they could to help members in need with heating supplies. The extreme cold was “a scary situation,” because much of the housing is of poor quality, said Chris Fairbanks, energy assistance program manager for the White Earth Band of Ojibwe in Minnesota.

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