New Jersey is about to experience its coldest weather in several years this week, but while that isn't terribly unusual for January, the likely reason for it is – suddenly warming temperatures miles above the Earth’s surface at the North Pole.

An arctic air mass is expected to spill across the United States and enter the northeast on Sunday, dragged by a series of cold fronts that are forecast to drop high temperatures into the low- to mid-20s by mid-week, according to the National Weather Service.

“It should be the coldest period of the winter season, so far,” wrote Dean Iovino, a meteorologist with the National Weather Service at Mount Holly. “Daytime highs are expected to be mainly in the 20s (Tuesday through Thursday), with some readings in the lower 30s in the far south. Maximum temperatures in the teens are anticipated for the elevated terrain up north.”

Temperatures overnight Tuesday and Wednesday could drop to the single digits in some places and any accompanying wind could easily push the wind chill below zero.

Climate researchers say the sudden cold snap is the result of a sudden warming in the stratosphere, some 60,000 to 80,000 feet above the Earth’s surface, near the North Pole that began in early January.

Typically, a persistent and strong large scale cyclone known as the polar vortex hovers near the North Pole during the winter months. But, as Judah Cohen, director of seasonal forecasting at Atmospheric and Environmental Research (AER) in Massachusetts, told Climate Central's Andrew Freedman, when the stratosphere suddenly warms it can split the polar vortex in two, and push arctic air south into the United States and Eurasia.

“So when the warm air rushes the pole it displaces the cold air over the pole and forces it equatorward,” Cohen told Climate Central.

While this process began in early January, the United States is only beginning to feel the effects of that now. By Wednesday, temperatures in New Jersey could be the coldest since 2009, according to Hackettstown-based weather firm WeatherWorks.

“We’re not just talking about your typical run-of-the-mill cold either,” said Nick Troiano, a long-range weather expert at WeatherWorks.

Across the Northern Plains and parts of New England, temperatures could drop to 20 degrees below zero. While New Jersey will only experience high temperatures in the teens and 20s, it will still be 10 to 15 degrees below normal, according to data from the New Jersey State Climatologist’s Office.

While the cold pattern may relax somewhat by week’s end and allow temperatures to moderate, Troiano said, overall, colder-than-average temperatures may largely persist through February.

“Although the heart of heart of this arctic air mass is expected to exit the region by the end of next week, temperatures are expected to average out colder than normal into the first half of February,” Troiano said.

While the cold will be in place, New Jersey is expected to remain relatively dry, at least until the end of the week, according to the National Weather Service. Some snow showers could affect the northern half of the state on Monday and Monday night, but aren’t expected to produce much accumulation.

A more significant system could affect New Jersey by the weekend, but the storm remains too far in the distance for a reliable forecast at this point.

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