BOSTON >> The arctic air that descended on the Northeast on Saturday brought dangerously cold sub-zero temperatures and wind chills to the region, including a record-setting wind chill of minus 108 degrees Fahrenheit (minus 78 C) on the summit of Mount Washington in New Hampshire.

In addition to the U.S. record low wind chill, the Mount Washington Observatory at the peak of the Northeast’s highest mountain, famous for its extreme weather conditions, recorded an actual temperature of minus 47 (minus 44 C), tying an observatory record set in 1934, while winds gusted to 127 miles per hour (204 kmh).

Across the rest of the region, wind chills — the combined effect of wind and cold air on exposed skin — dropped to minus 45 to minus 50 degrees Fahrenheit (minus 43 to minus 45 C), the National Weather Service reported.

The current method to measure wind chill has been used since 2001.

“This is just kind of an Arctic intrusion,” said Stephen Baron, a meteorologist with the National Weather Service in Gray, Maine. “Sometimes in the winter the Jetstream dips and the Arctic oscillation allows the cold air to come into our area for a day or two.”

The high winds were blamed for the death of an infant in Southwick, Massachusetts, on Friday.

The winds brought a tree branch down on a vehicle driven by a 23-year-old Winsted, Connecticut woman, according to the Hampden district attorney’s office. The driver was taken to the hospital with serious injuries, but the infant died, authorities said.

Most people heeded warnings to stay inside on Saturday, but some people ventured out.

Gin Koo, 36, braved the cold to take his Boston terrier, Bee, out for a necessary walk.

“I can’t remember it being this cold, not since 2015,” said Koo, who was wearing three shirts and a down jacket, as well as a hat and a hood. Bee still shivered despite his doggie coat. “I wouldn’t go out if I didn’t have to.”

Paul Butler, 45, who has been homeless since he was evicted in December 2021, took shelter in South Station, the Boston transit hub that authorities kept open overnight so unhoused people had somewhere warm to sleep.

“This is the coldest I ever, ever remember, and I worked the door at a bunch of clubs for 15 years,” said the former Marine.

Boston’s Pine Street Inn, the largest provider of homeless services in New England, ramped up outreach to those on the streets, doubling the number of vehicles that could transport people to shelters and opening their lobby to provide extra space.

“On a night like last night, the biggest concern is the people who have compromised judgment,” President and CEO Lyndia Downie said Saturday of people who have substance use disorder or mental illness. “On these cold nights, they are not thinking at 100% of their capacity. Those are the people we are most worried about.”

The emergency room at Massachusetts General Hospital treated several people for hypothermia overnight and a couple were admitted for frostbite.

“The reason that people unfortunately end up with severe frostbite in most cases is just because they don’t have anywhere warm and safe to go,” said Dr. Ali Raja, deputy chair of the emergency department.

Several cities, including Boston; Providence, Rhode Island; Hartford, Connecticut; Worcester, Massachusetts; Albany, New York; and Glens Falls, New York set or matched record low temperatures for Feb. 4, according to the National Weather Service.

The cold curtailed some traditional winter activities. Organizers of an annual ice castle attraction in North Woodstock, New Hampshire shortened the evening visitor schedule for Saturday night.

Erin Trotta of Massachusetts, who had already booked a visit still planned to go, but was taking extra steps to stay warm.

“We are prepared to take on the polar vortex ice castles. … Snow pants, thick winter coats, hand and foot warmers, face masks, the kind where only your eyes are exposed, and good gloves and winter boots. Plan to drink some hot cocoa to keep warm.”

In New York’s Adirondack Mountains, Old Forge recorded a temperature early Saturday of minus 36 degrees (minus 38 C) degrees. Temperatures plunged into the negative teens in dozens of other cities and towns, with wind chill making it feel even colder.

Mackenzie Glasser, owner of Ozzie’s Coffee Bar in Old Forge, said frigid temperatures are just part of living in the Adirondacks.

“I even had customers for the first hour that I was open, and I wasn’t expecting that at 7 a.m. So I don’t think it’s keeping too many people away,” she said.

The good news is that the cold air is expected to move out of much of the region by Sunday, when temperatures could rise to the 40s.

“That’s quite a change,” the National Weather Service’s Baron said.

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Michael Hill in New York and Kathy McCormack in Concord, New Hampshire contributed to this story.