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How will the polar vortex play a role in upcoming pattern change in eastern US?

AccuWeather logo AccuWeather 4 days ago Alex Sosnowski

A change and reality check is coming soon in the weather pattern that will allow longer-lasting, more frequent waves of cold air to roll across the eastern half of the United States.

"We expect conditions to turn much colder during the last two weeks of January," AccuWeather Lead Long-Range Meteorologist Paul Pastelok said.

"There will be some weakening and stretching of the polar vortex, which will allow cold air to drain southward from Canada in stages during the second half of the month. However, a big breakdown and major shift of the polar vortex, which would allow an extremely cold discharge, is not anticipated," he explained.

The polar vortex is a large storm that tends to keep cold air locked up near the Arctic Circle when it's strong. When the polar vortex weakens and shifts its position, cold air can escape southward.

A major plunge or shift of the polar vortex is not needed for lasting harsh cold this time of the year.

The weather pattern during the late autumn and thus far during winter has only allowed brief bursts of cold air to dip south, mainly across the northern third of the nation, with one or two exceptions.

The upcoming cold could be enough to shock Northeasterners who are riding a temperature roller coaster this week. Recall that last weekend, a large northward bulge in the jet stream developed in the Eastern states. This allowed a southerly flow of warm air that contributed to dozens of records over a broad area as well as severe weather in the South. Temperature departures from average ranged from 15 to 30 degrees Fahrenheit above normal up and down the Eastern Seaboard with highs ranging from 40 to 80.

a close up of a map © Provided by AccuWeather

This week, the jet stream has resumed a pattern similar to much of December and early January. The jet stream will continue this pattern of short northward bulges and southward dips into this weekend until a large winter storm arrives.

With the aid of this large storm and weakening of a high pressure area off the Atlantic coast near Bermuda, the jet stream pattern will continue to evolve in such a way that a large southward bulge will set up by next week. Instead of the pattern flipping back to small bumps and dips, the large southward bulge is likely to persist and stick around for two to perhaps four weeks.

a close up of a map © Provided by AccuWeather

"By next weekend, nearly all of the Lower 48 states may be colder than average," Pastelok said.

However, temperatures are not forecast to plunge to extreme enough levels to balance the record warmth from this past weekend.

"Temperature departures from average will probably be more like 3 to 10 degrees below average," Pastelok said. "That's a far cry from the 15- to 30-degree departures on the warm side."

But, given that the upcoming period is close to the coldest part of the winter, the pattern change will be a harsh reality check for hundreds of millions of people.

Energy demands will increase and heavy winter coats with hats and gloves will make a comeback.


During late January, average high temperatures range from the middle teens at International Falls, Minnesota, to near 32 in Chicago, the upper 30s in New York City, the middle 50s in Atlanta, the middle 60s in New Orleans and the lower 70s in Orlando, Florida.

"Despite the upcoming colder-than-average weather forecast for the latter part of January, temperatures for the month as a whole would still finish well above average due to the warmth that occurred during the first half of the month," Pastelok said.

The colder trend is expected to continue into February, and AccuWeather's long-range team of meteorologists is predicting February to average 1 to 3 degrees below normal for much of the eastern half of the nation, with the exception of Florida.

"As we get into February, the polar vortex may strengthen and retreat toward the Arctic Circle once again and the jet stream dip may set up more toward the middle of the nation, which would suggest cold conditions there but result in moderating cold in the East," Pastelok stated.

Since water temperatures in the nearby western Atlantic tend to reach their lowest point during February, it may be much easier for snow to fall in the Northeast Interstate 95 cities with the anticipated pattern.

The cold pattern may leave many wondering whether any major East Coast snowstorms could come calling, in a winter where snow seems to be absent. Forecasters say the pattern may allow periodic storminess, perhaps with some snow, but an atmospheric traffic jam would have to develop over the Atlantic Ocean first for a big one to come about later.

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