The near-record-breaking cold is expected to tighten its grip on the region in the coming days, threatening to turn what is normally a celebratory weekend into a dangerous one.
Fans who cheer the Eagles and jeer the Cowboys on New Year's Eve at Lincoln Financial Field or watch fireworks on the Delaware River waterfront will do so with temperatures likely to hover in or just above single digits, meteorologists say.
And revelers who plan to line Broad Street on Monday morning or march wearing fabulously ridiculous costumes for the Mummers Parade could be doing so amid a wind-chill that makes it feel like zero. (Parade officials and the city are discussing whether to postpone the parade.)
If predictions hold, the new year will arrive during what is shaping up to be the region's longest stretch of below-freezing weather in 13 years. And if those temperatures continue beyond Thursday — which is likely — the deep freeze will be the longest since 1989.
"Make sure you're dressed properly and everything is covered," Dean Iovino, a National Weather Service meteorologist in Mount Holly, advised revelers Thursday. "There is a risk of frostbite if your skin is exposed to those temperatures for long."
The impact was already starting to ripple.
SEPTA suspended service Thursday on the Manayunk/Norristown Regional Rail line and the Chestnut Hill East line due to overhead power line issues that transit officials suspected were caused by the subfreezing temperatures. NJ Transit suspended service Thursday morning on a stretch of the Atlantic City Rail Line because a bridge across the Delaware River was stuck in the up position.
And predictions for extreme cold forced Ocean City and Ventnor, Atlantic County, to cancel their traditional New Year's Day polar bear plunges.
Temperatures won't quite drop to record-breaking levels as revelers ring in 2018. But they'll be close. The region set a record in 1881 when the low for New Year's Day was 4 degrees.
But as fireworks burst over the Delaware on Sunday night, the temperature in the city will hover around 15 degrees and the mercury will drop into single digits in the outer suburbs.
Those temperatures will linger on New Year's morning, when the wind chill will be around zero. The high for the day will struggle to reach 20.
But the cold weather is not deterring Pennsylvania state park officials from leading the seventh annual First Day Hikes on New Year's Day. Terry Brady, spokesman for the state's Department of Conservation and Natural Resources, said freezing temperatures can present opportunities for hikers to see animals behaving differently. But he encouraged hikers to call their parks to make sure they are participating.
Since Christmas morning, Philadelphia has been under a "Code Blue" designation, which means temperatures feel near 20 degrees and city officials make extra efforts to find shelter for homeless people. Surrounding counties have made similar declarations.
David Holloman, spokesman for the city's Office of Homeless Services, said more people come to shelters during extended Code Blue periods like this one, "which is a great thing because it gives us an opportunity to address individuals who are chronically homeless who otherwise would not come in."