The polar vortex had a record early warping that could lead to a chillier pattern in parts of the U.S. as soon as Thanksgiving week, possibly lasting into early December.

What is the polar vortex?

The polar vortex is a swirling cone of low pressure over the poles in the colder months high in the atmosphere.

How high? Try anywhere from 4 to 31 miles above the ground, in an atmospheric layer called the stratosphere. That's higher than where most of the weather you're familiar with happens.

Almost 13 years ago, the "polar vortex" entered into pop culture during a January 2014 cold outbreak. But scientists have known about it for many years, even before the Civil War.

(MORE: Learn about the polar vortex)

What just happened with the polar vortex?

The polar vortex can vary in strength, shape and location throughout the colder months.

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When it's strong, centered over the pole and circular, it tends to lead to weather patterns that keep any cold air bottled up in the far north.

But in early November, the vortex became much weaker, was pushed off the North Pole and stretched like a rubber band.

That's often caused by a sudden stratospheric warming (SSW). By sudden, we mean temperatures in the stratosphere can sometimes skyrocket by up to 50 to 70 degrees or more in just a few days.

In this case, the SSW was strong enough to reverse stratospheric winds over the Arctic regions from their normal westerly direction to light easterly, in what meteorologists call a major SSW event.

This was the earliest major SSW in records dating to 1958. The two other November events happened in late November 1958 and 1968.

Most of these events happened in January or February. That's when the polar vortex is well established, but more easily disturbed by the large-scale waves lower in the atmosphere that push upward.

Why could this change in the polar vortex matter?

Cold air can and does plunge into the U.S. and Europe without hiccups in the polar vortex.

While it doesn't always happen, these warps in the polar vortex and warmer stratospheric air can slowly leak downward and eventually affect the jet-stream pattern that drives our weather.

Think of it like you're throwing red paint at a blank canvas on the wall. Eventually that red paint — the warmer stratospheric air — drips down the canvas, as it can into the lower atmosphere.

And when that warmer air drips down, blocking patterns may eventually set up that influence the persistence of cold air masses weeks later. In this case, that could happen sometime in late November or early December.

One such pattern that can set up is called a Greenland block, pulling more persistent colder air into the eastern U.S.

(MORE: The latest November outlook)

Will the weather pattern turn colder?

There are often many factors in the atmosphere that influence the weather pattern.

This record-early polar vortex weakening could help set up the blocking pattern discussed above that delivers colder air to at least the northern U.S. sometime in late November.

Another blocking pattern over the Pacific Ocean and western North America — the negative phase of the Eastern Pacific Oscillation — could also push colder air into the U.S.

Apart from those ingredients, long-range forecast models suggest a more active weather pattern Thanksgiving week could initially pull cooler air southward into the U.S.

(MAPS: 7-day US forecast rain, snow)

But there are also conflicting signals.

First, it's not that cold in Canada and the Arctic.

Snow cover over North America is the third lowest for this time of year in 28 years, according to Matthew Williams, energy meteorologist at The Weather Company. That's a key factor to refrigerate cold air that plunges into the U.S.

The elephant in the room is what is likely to be a record-strong El Niño exerting a heavy influence on the weather pattern through the winter.

(COMPLETE COVERAGE: Super El Niño)

Once the polar vortex returns to its normal shape, it could work in tandem with El Niño to wall off cold air from the northern U.S. for the rest of December, leading to the warmer North pattern we've seen so far through much of fall.

The short answer appears to be:

• It could turn colder for some in the U.S. in late November.
• That cold could linger into early December.
• But then it will probably warm back up for the rest of December.

What should you do?

This is an uncertain forecast given the conflicting signals we discussed.

If it has felt warmer than usual in your area in recent weeks, be prepared for it to turn colder for a couple of weeks from Thanksgiving week through early December.

Late fall tasks you might want to do sooner rather than later include:

• Shut off water to your outdoor faucets to avoid freezing.
• Finish raking leaves and any other lawn cleanup before it turns colder.

(MAPS: 10-Day US forecast highs and lows)

Jonathan Erdman is a senior meteorologist at weather.com and has been covering national and international weather since 1996. Extreme and bizarre weather are his favorite topics. Reach out to him on Bluesky, X (formerly Twitter) and Facebook.