A powerful arctic blast swept into the U.S. Northeast on Friday, pushing temperatures to perilously low levels across the region, including New Hampshire's Mount Washington, where the wind chill dropped to 105 degrees below zero Fahrenheit (-79 Celsius), forecasters said.

Wind-child warnings were posted for most of New York state and all six New England states - Massachusetts, Connecticut, Rhode Island, New Hampshire, Vermont and Maine - a region home to some 16 million people.

The National Weather Service (NWS) said the deep freeze would be relatively short-lived, but the combination of numbing cold and biting winds gripping the Northeast would pose life-threatening conditions well into Saturday.

Schools in Boston and Worcester, Massachusetts, New England's two largest cities, were among those closed on Friday over concerns about the risk of hypothermia and frostbite for children walking to school or waiting for buses.

Boston Mayor Michelle Wu declared a state of emergency through Sunday and opened warming centers to help the city's 650,000-plus residents cope with what the NWS has warned was shaping up to be a“once-in-a-generation” cold front. The bitter cold forced a rare closing of a floating museum that presents a daily re-enactment of the 1773 Boston Tea Party, when a band of colonists disguised as Native Americans tossed crates of tea taxed by the king into Boston Harbor in protest.

"It's too cold for that, we're closed,” a receptionist at the museum said on Friday. Early on Friday, the arctic surge flowing into the United States from eastern Canada was centered over the U.S. Plains, weather service forecaster Bob Oravec said. Kabetogama, Minnesota, near the Ontario border, was America's coldest spot at 1 p.m. EST, with a temperature of minus 39 F (-39.5 C).

Sub-freezing, blustery conditions spread eastward through the day, sending wind-chill factors - measuring the combined effect of wind and cold on the body - plunging into the -40s across much of Maine, NWS meteorologist Brian Hurley said.

In Mount Washington State Park, atop the Northeast's highest peak, temperatures fell to minus 45 F (-46 C) Friday evening, with sustained winds of 90 miles per hour driving wind chill to 105 below zero F (-76 C), according to Hurley.

By comparison, air temperatures in Eureka, Canada's northernmost Arctic weather station, were hovering at -41 F (-41 C) on Friday morning. Boston was at 8 degrees F (-13 C) on Friday evening, while in Worcester, Massachusetts, 40 miles (64 km) to the west, the mercury hit 3 F (-16 C), with temperatures expected to fall even lower, Hurley said.

Record cold was expected in both cities on Saturday. Forecasts called for a low of -6 F in Boston, exceeding an 1886 record -2 for the date. Worcester was headed for a low of -11 on Saturday, which would break its previous 1934 record of -4 for the date.

"BEFORE THE REAL COLD HITS”

Despite the extreme cold, Nhon Ma, a Belgium native, was out on Friday with his Zinneken's food truck near Boston University selling Belgian waffles made from homemade dough, and keeping warm with three or four waffle irons going at once. ”Those create heat, but of course it's cold, it's going to be cold, but we're here,” Ma said.

In a frigid Biddeford, Maine, about 95 miles (150 km) north of Boston, Katie Pinard, owner of a coffee and book shop, said business was brisk as customers came in from the cold, with some opting to work from her shop, Elements: Books Coffee Beer, rather than commute. ”Yeah, Mainers are pretty hardy, but talk to me tomorrow and we'll see if we're busy or not,” she said, looking ahead to Saturday morning, when temperatures were expected to drop to -18 F (-28 C).“I think people are out and doing what they need to get done before the real cold hits.”

While the Northeast was hunkering down, Texas and parts of the South were starting to warm up in the aftermath of a deadly winter ice storm that brought days of freezing rain, sleet and ice, causing massive power outages and dangerously icy roads. But the weather was warming up, with temperatures in Austin, Texas, expected to hit 52 F (11 C) on Friday and 71 F (22 C) by Monday, forecasts say.

Meanwhile, a Pacific storm was expected to bring another round of heavy snow to California's Sierra Nevada mountains on Saturday night.

Periods of moderate rainfall were forecast in lower elevations of central and northern California and the Pacific Northwest through the weekend.