Temperature some 15 to 30 degrees lower than normal will grip much of the eastern two-thirds of the nation up to seven to 10 more days. Some parts of the north central United States could see temperatures an astonishing 40 to 50 degrees colder than normal this weekend.

On the morning of New Year’s Day, the National Weather Service predicts the nation’s average low temperature to hover around 10 degrees, with about a third of locations below zero.

These temperatures, compared to normal, will be the coldest in the world.

The bitter chill first arrived around Christmas Eve and has only dug in, becoming more frigid over time, breaking records from the Upper Midwest to the Northeast:

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A few small towns in northern Minnesota were as cold as minus-40 degrees Wednesday morning. Mount Washington, N.H. saw its wind chill plunge to minus-88 on Thursday morning.

As this cold air spilled over the Great Lakes, it generated incredible snowfall, including 65 inches in Erie, shattering the Pennsylvania two-day snowfall record, and up to 62 inches in Oswego County, N.Y.

The piercing cold over the Upper Midwest and Great Lakes is pouring into the Northeast, where the National Weather Service predicts record-cold high temperatures Thursday. Highs are only expected to reach 10 to 15 degrees in Boston, about 20 in New York and 25 in Washington.

The final week of the year in Boston is shaping up to be about the coldest in recorded history.

The pinnacle of this unforgiving cold snap is likely to occur between this weekend and the first few days of the New Year, progressing from the Dakotas to the Northeast. On Saturday, some parts of eastern Montana, the Dakotas and northern Minnesota may see air temperatures crash to minus-40 degrees, and wind chills to minus-50 or lower. High temperatures may not exceed minus-10 Saturday, which would threaten some records.

On Saturday and Sunday, Minneapolis is forecast to have highs of only about minus-5, with lows near minus-15. Wind chills will be considerably lower, as cold as minus-30. Chicago may see its highs stuck in the single digits both Saturday and New Year’s Day.

In the East, 2018 may start off even colder than the close of 2017. The American and European model predict New York City will ring in the New Year with an air temperature near 10 degrees and wind chills of zero to minus-5. This would rank among the coldest ball drops in the Big Apple in recorded history. The last time it was so cold was in 1962; 1917 marked the coldest ball drop, when the air temperature was a mere 1 degree.

Subzero wind chills are likely to cover enormous territory New Year’s Day — extending as far as south as Oklahoma, Arkansas and the central Appalachians.

Just how cold will your city be? Here is the European modeling system’s (ensemble mean) forecast for the coldest day between Dec. 30 and Jan. 2:

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Minneapolis: Sunday. High: Minus-4, low: minus-16

Milwaukee: Monday. High: 8, low: minus-2

St. Louis: Monday. High: 14, low: 0

Oklahoma City: Monday. High: 23, low: 12

Dallas: Monday. High: 31, low: 23

Chicago: Monday. High: 5, low: minus-10

Detroit: Sunday and Monday. High: 10, low: minus-9

Cleveland: Monday. High: 9, low: 0

Indianapolis: Monday. High: 5, low: minus-9

Memphis: Monday. High: 26, low: 14

Boston: Monday. High: 9, low: minus-2

New York: Monday. High: 17, low: 5

Pittsburgh: Monday. High: 15, low: 2

Washington: Monday. High: 22, low: 12

Raleigh, N.C.: Tuesday. High: 28, low: 19

Atlanta: Tuesday. High: 33, low: 20

Note that while we are confident it will be extremely cold, forecasts are likely to change some over the coming days. Models have tended to predict somewhat colder temperatures than reality this year at long lead times. But even if these predicted temperatures are a little colder than what actually materializes, it will still be bone-chilling cold.