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Unforgiving cold snap will engulf eastern two-thirds of the nation through New Year’s Day

Temperature forecast difference from normal Wednesday morning to Monday morning from GFS model.

For many parts of the nation, a prolonged period of punishing cold is just getting started.

The cold snap that descended on much of the nation from the Rockies eastward on Christmas Eve is predicted to become further entrenched and even more biting in the coming days. The worst of the cold may grip the central United States from Saturday through New Year’s Day, when temperatures may fall more than 30 degrees below normal. Then it may spill eastward.

Some of the cold could be record-challenging if the most extreme forecasts are correct.

It’s already brutal

The first cold wave arrived over the weekend into Christmas Day, infiltrating the Pacific Northwest, the Northern Rockies and much of the eastern half of the nation.

The initial blast of cold supported snow that blanketed half the nation Christmas Day, the highest percentage on Dec. 25 in five years. For the first time on record, Seattle had at least an inch of snow on the ground for both Christmas Eve and Christmas Day. Meanwhile, thundersnow rocked Boston while a blizzard warning was hoisted for southeast Maine.

As the Arctic air poured over the Great Lakes, it produced astronomical snowfall amounts. An incredible 53 inches of snow piled up in 30 hours in Erie, Pa., Pennsylvania’s biggest two-day snowfall on record.

How this Pennsylvania city got more than 4 feet of snow in just 30 hours

On Tuesday morning, a reinforcing blast of cold sent windchill temperatures across North Dakota and northern Minnesota crashing to around minus-40, offering just a taste of even more bitter cold to come.

Worst is yet to come

The extreme cold over the north-central United States on Tuesday will ooze into the Northeast by Thursday, when the National Weather Service predicts record-cold high temperatures from the Delmarva to New England, from the 20s south to the single digits north.

But it’s the surge of cold that follows, expected to be unleashed this weekend and to continue into early next week, that may be even more severe — particularly in the central United States.

Jason Furtado, a meteorology professor at University of Oklahoma, described the forecast as “about as anomalously cold as it gets” in a tweet.

The same areas of North Dakota and Minnesota witnessing minus-40 windchills Tuesday may see these levels plummet to between minus-50 and minus-60 by the weekend.

Taylor Trogdon, a meteorologist at the National Weather Service, tweeted that the American model is forecasting some of the most extreme cold “ever observed” in central Missouri, with highs below zero and lows near minus-20 around New Year’s.

This frigid air may well expand east into the Mid-Atlantic and the Northeast by New Year’s Day or shortly thereafter.

The cold waves, together, could become noteworthy for their intensity and duration. The National Weather Service is calling for New York City’s average temperature over the next seven days to be around 19 degrees, which is about 10 degrees below average.

Just how cold will your city be? Here is the American modeling system’s (ensemble mean) forecast for the coldest day between Wednesday and New Year’s Day:

  • Minneapolis: Saturday. High: minus-9, low: minus-15
  • Milwaukee: Saturday. High: 6, low: minus-2
  • St. Louis: Sunday. High: 1, low: Minus-9
  • Oklahoma City: Monday. High: 9, low: minus-1
  • Dallas: Monday. High: 20, low: 11
  • Chicago: Saturday. High: 4, low: minus-1
  • Detroit: Monday. High: 14, low: 4
  • Cleveland: Monday. High: 15, low: 11
  • Indianapolis: Monday. High: 6, low: minus-5
  • Memphis: Monday. High: 16, low: 9
  • Boston: Wednesday. High: 11, low: 6
  • New York: Monday. High: 17, low: 6
  • Pittsburgh: Monday. High: 15, low: 4
  • Washington: Monday. High: 20, low: 10
  • Raleigh, N.C.: Monday. High: 26, low: 15
  • Atlanta: Monday. High: 35, low: 20

Keep in mind that model forecasts, so far this year, have tended to run colder than reality beyond three days into the future. So it remains to be seen whether the cold will be this intense.

But irrespective of its exact magnitude, models are in strong agreement that the abnormally cold period will last for a while — at least the next week to 10 days. After that, there may be a gradual thaw.

A prolonged period of bitter cold will be moving through many parts of the country as 2017 comes to an end. (Video: Claritza Jimenez/The Washington Post)