ST. PAUL, Minn. -- A bracing wave of Arctic air swept across much of the nation on Wednesday, suddenly turning what had been a relatively mild winter into a shivering misery that has caused several deaths in the Midwest and prompted cities along the Eastern Seaboard to open emergency shelters.
The freezing weather, which arrived in the Midwest late last week, has plunged temperatures to record lows in portions of the northern tier of the country, chilling even those well adapted to frigid winters.
International Falls, Minn., the self-proclaimed Icebox of the Nation, reached a high of 5 degrees below zero on Wednesday before falling to an expected low of 32 degrees below zero, according to the National Weather Service. Factoring in wind chill, the low in International Falls, which is near the Canadian border, was expected to be 40 degrees below zero on Wednesday night.
Almost as cold were Duluth, Minn., on Lake Superior in the northeastern part of the state, where temperatures were forecast to drop to 17 below zero, and Minneapolis and St. Paul, in comparison, with an expected low of 7 degrees below.
Isaac Arreguin, 23, was waiting for a bus in St. Paul on Wednesday afternoon, having forgotten his scarf and gloves.
"I'm pretty O.K.," he said, sniffing. "It's the combination of the cold and the wind that's getting me."
Not far away, Terry Och, 47, a security guard, who was on duty near the Cathedral of Saint Paul, was putting on a braver face. His cold-weather armor? "Hat, hood, four coats, two long johns, four socks, gloves with the handwarmers inside."
"I love the winter," he said. "You got to like the cold to live in it and be out like this."
In Grand Forks, N.D., the deep chill was brushed aside as child's play, even as the forecast for the next three days predicted that temperatures would go no higher than 6 degrees on Thursday and fall to 16 degrees below zero on Friday.
"It is not unusual for us," said Brandon Boespflug, the city's fire marshal. "Anywhere a little south of here and it would stop everything, but this is normal weather. We're so used to it."
One hazard, though, Mr. Boespflug said, is that the city's water pipes sometimes freeze. This can pose a danger to people who live in trailer homes, because the pipes are easily accessible.
"People try to thaw it out themselves using torches or whatever they have handy, and, well, if anything is combustible, it goes," he said. "We haven't had it happen so far this winter, and I'm knocking on wood as I talk to you."
Among the areas that have set records in the last couple of days are the Chicago Botanic Garden, where the temperature earlier this week fell to 3 degrees below zero, and Cook County, Minn., where the temperature dropped to 34 degrees below zero, according to the National Weather Service. Lake-effect snowfall has deepened the chill, dropping more than 10 inches of snow this week in Kalamazoo, Mich.
Since Saturday, the authorities have reported at least four deaths related to the cold in the Midwest, including a 70-year-old man found frozen in his unheated home in Des Plaines, Ill., on Sunday, according to The Associated Press.
Forecasters said the cold weather could be accompanied by several inches of snow in portions of Illinois, Iowa, Michigan and Wisconsin, and snowfall is expected to extend east to New York and as far south as Virginia on Friday.
As the frigid air moved east, local officials tried to prepare. The anticipated high on Thursday was 11 degrees in Buffalo, and around 20 degrees in Cleveland and Boston.
Mayor Thomas M. Menino of Boston said on Wednesday that the city's adult emergency shelters would be kept open 24 hours a day for the duration of the cold snap.
"We were fortunate to have a mild winter last year, and we want to make sure people are safe now that we're seeing extremely cold weather in Boston again," he said in a statement.
In other parts of the country, temperatures were unseasonably warm. Cheyenne, Wyo., was in the 50s on Wednesday, and Pueblo, Colo., was in the low 70s.
This article originally appeared in The New York Times.