An arctic blast from Canada is responsible for some of the frigid temperatures in the northern U.S. and some of the coldest air to hit the Northeast in two years.
The cold was linked to at least two deaths in the Northeast, including that of a woman whose frozen body was found in a driveway.
Temperatures were projected to fall well below zero across New England on Sunday night as a high-pressure area builds over the region. The coldest spots will dip to less than 30 degrees below zero, with the wind chill expected to drop to 51 below zero in some places, the National Weather Service said.
"This is the coldest air we've had in about two years," said Michael Hill, a weather service meteorologist in Caribou, Maine.
Emergency management agencies were urging residents to bundle up and heat their homes safely. Shelters were preparing for an increase in the number of people wanting to get out of the cold, and authorities in Maine and Pennsylvania waived restrictions on heating oil delivery.
Northern New England is used to cold winters; a remote site in northern Maine recorded a minus 50 reading on Jan. 16, 2009, that tied a 1933 record set in Vermont for the coldest temperature recorded in New England.
But last year's relatively warm winter provided a respite from the dangerously cold temperatures that are being forecast for early this week. Temperatures are expected to rise somewhat Tuesday before reaching seasonable levels Wednesday.
Though a high of 24 was forecast for New York's Central Park on Sunday, wind chills made daytime temperatures feel more like 3 to 7.
The National Weather Service predicted a high of 19 on Monday, meteorologist Joe Pollina said. That's the coldest it's been in New York City since Jan. 16, 2009, when the high was 16.
In Philadelphia, the city extended an alert issued Thursday that gives officials the power to go out onto the streets and bring in homeless people to shelters because the weather conditions pose a threat of serious harm or death.
About 90 miles northwest of Philadelphia, a man died after spending the night in his car in frigid temperatures in Lansford, and his wife found him Saturday morning. Temperatures had dropped into the single digits overnight, Lansford police Detective Jack Soberick said, but it's unclear why 49-year-old Alan Kurtz had slept in his car.
In North Haven, Conn., a woman's frozen body was found in a home's driveway Sunday morning after a neighbor called police. Denise O'Hara apparently fell in a driveway and froze to death Saturday night, when temperatures were close to zero, police said.
In Pittsburgh, where the Pittsburgh Steelers took on the New York Jets in the NFL playoffs Sunday evening, the temperature was about 13 degrees at game time.