As we wave goodbye to 2015, we do so, too, to the stretch of extraordinarily balmy days that have resulted in December’s being 12.7 degrees above the monthly norm.

The National Weather Service and others are indicating a shift in the weather pattern as 2016 gets rolling, meaning a higher probability for normal temperatures — and possibly below normal temperatures — for the beginning of January.

Think of it as a return to what’s “more seasonable,” said Jay Engle, weather service meteorologist in Upton.

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Look for “cold weather to kick off 2016,” said Rich Hoffman, News 12 Long Island meteorologist. “When people go back to work on Monday, Jan. 4,” he said, temperatures in the morning are expected to be in the 20s, with a high of around 38, based on Wednesday’s forecast.

That would be right about on target for the first week of January, he said, when highs average out to close to 40 and lows near 24.

This early-in-the-month move to more seasonable air, a mix of polar and that from the Pacific, is being brought about by a southward dip in the jet stream, said Paul Pastelok, head of long-range forecasting at AccuWeather.com. But he and his team have their eyes also on factors that may well lead to a real blast of Arctic cold around mid-month.

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On Wednesday a massive storm over Iceland was “drawing up a tremendous amount of warm air from the lower latitudes,” set to create “a huge upper level high of warm air” over areas bordering the Arctic Circle. Meanwhile, another upper level high was building over western Canada, with the two expected to attempt a merger over the Arctic in the Jan. 8 to 10 time frame.

That, in turn, would disrupt the strong winds now keeping the coldest air locked in over the pole, he said, with some of that cold expected to escape to the south, dipping down to the Ohio Valley and the Northeast.

Though there are other schools of thought, Pastelok said his team is expecting this mid-month blast to be transient, sticking around for just a few days and not settling in for a lengthy visit as was seen in the past two winters.