(NEW YORK) — A significant change in the atmosphere means the weeks after Thanksgiving could be colder and snowier than normal across portions of the United States.

It’s all thanks to a disruption in the polar vortex. Here’s what you need to know.

Why is this happening?

Our atmosphere consists of many layers of moving air; the troposphere is where our weather happens and above it is the stratosphere. Over both poles, a ring of strong mid-level winds called the polar vortex traps cold, sub-arctic air.

There are two of these polar vortexes — one in the troposphere that affects weather every winter, and one in the stratosphere that contains much colder air but only affects the surface weather during winter less frequently.

When polar vortex winds are strong, this frigid air remains near the poles. But when the polar vortex is weak and is disturbed, the frigid air can spill out from the North Pole, down south towards the surface.

Scientists are still trying to understand these disturbances and why they occur, but they can drive the most intense cold-air outbreaks and winter weather bursts in the U.S.

Sometimes, the polar vortex simply stretches out, bringing quick bursts of cold air and some wintry weather to the U.S. In more extreme cases, a phenomenon called “sudden stratospheric warming” — or SSWs — can trigger more significant disruptions to the polar vortex.

While it may seem counterintuitive, a sudden warming in the stratosphere above the poles often weakens these winds, disrupting the polar vortex and allowing cold air to spill out from the North Pole and down into places like the U.S., Europe and Asia.

These events can take weeks to unfold and can have cascading impacts. Some of these events can lead to strong cold outbreaks and snowier spells, while others have little impact near the surface.

According to Dr. Amy Butler, a meteorologist and lead of the Stratospheric Modeling & Analysis program at National Oceanic Atmospheric Administration, SSWs occur once every other winter, But “there are only one to two major events in late November in the record back to 1958.”

“We have this unprecedented disruption in the polar architecture where it’s so early in the season … There’s not many past analogs to draw from and say [with confidence] about how this is going to go,” said Dr. Judah Cohen, a climatologist at MIT and the director of seasonal forecasting for Atmospheric and Environmental Research (AER) at the JANUS Research Group.

Cohen added that an SSW is not a given yet and that we could simply see the polar vortex be stretched out past Thanksgiving, but it would still result in a noticeable change to colder and possibly more wintry weather for parts of the U.S.

La Niña will also play a role in this pattern shift, as will the forecasted weather conditions for the winter ahead.

“With North America, we have a weak La Nina and other patterns in the Pacific that have a direct influence on the weather as well,” said Dr. Jason Furtado, associate professor in the School of Meteorology at the University of Oklahoma. Furtado also added that these, consequently, lead to a higher chance of a colder December.

What does it mean for the forecast?

Long-range forecasts from NOAA’s Climate Prediction Center favor below-average temperatures for the majority of America from late November into December.

However, this outlook deals with average temperatures over the period, so they don’t account for short-term variations that occur over days or weeks — meaning there could be a cold snap for a few days then warmth for the rest of the period, with the average leveling out or warmer.

What does it mean for snow?

These disturbances to the polar vortex can plunge cold air south and often create more chances for snow. However, the relationship between these two is not as straightforward.

According to NOAA, this pattern change supports more winter-like conditions across the central U.S. and increase the potential for heavy snow. Specifically, the increased potential for heavy snowfalls along the Great Lakes, a region historically known for lake-effect snow.

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(WASHINGTON) — As President Donald Trump pushes Ukraine and Russia to commit to a peace deal before Thanksgiving, both leaders suggested they would engage on it but signaled doubts it could succeed.

Ukraine’s President Volodymyr Zelenskyy warned his country may face a difficult choice between losing its “dignity” or the support of its most important ally –presumably the United States, though Zelenskyy didn’t mention by name — as the Trump administration pressured Kyiv to accept the plan that would impose harsh concessions on Ukraine and that many Ukrainians fear would be effectively a capitulation.

Russian President Vladimir Putin said the deal, which Russia has helped develop and contains many of its key demands, could serve as a “basis” for a solution to the conflict, but accused Kyiv of being unwilling to accept it.

Zelenskyy addressed the nation in a powerful speech, where he vowed not to betray the country and said the next week would “be very difficult.”

Trump’s 28-point peace plan demands provisions that the Kremlin has long demanded and that have been previously dismissed as non-starters for Kyiv, including that Ukraine cut its armed forces by more than half and cede swaths of territory not yet occupied by Russia, according to a draft proposal obtained by ABC News.

Officially, the 28-point peace plan notes that “Ukraine will receive reliable security guarantees,” which a senior U.S. administration official told ABC News included a NATO-style security guarantee. Under that provision, the U.S. and its allies could respond with military force if Russia attacks Ukraine in the future, according to the official.

The plan comes after Ukraine suffered heavy losses in the last few weeks and Russian forces captured more territory. Zelenskyy himself is currently under pressure because of the worst corruption scandal of the war that involves top officials, which has rocked his administration.

Zelenskyy said Ukraine is facing “one of the most difficult moments in our history” and that Ukraine in the coming days may have to choose between “dignity” and the “risk of losing a key partner.”

“Either complicated 28 points, or an extremely tough winter — the toughest — and further risks. A life without freedom, without dignity, without justice,” he said.

Zelenskyy compared the current situation to the first days of the war, when he refused to flee and Ukrainians held back Russia.

“They said: either this, or nothing. Either you sign this, or you will simply be eliminated. We did not betray Ukraine then; we will not do it now. And I know for certain that in this truly one of the hardest moments of our history, I am not alone,” he said.

Zelenskyy spoke with Vice President JD Vance about the plan on Friday.

“We managed to cover a lot of details of the American side’s proposals for ending the war, and we’re working to make the path forward dignified and truly effective for achieving a lasting peace,” a readout from the Ukrainian president read.

Putin, in a meeting with his national security council that was televised, said Russia was in possession of the 28-point plan and suggested Moscow was prepared to take it as a basis for “a final peace settlement” but had yet to discuss it in detail.

Putin said Russia had previously discussed a version of the plan with the Trump administration around his and Trump’s summit in Alaska this summer, calling the 28-point draft an “essentially modernised” one.

“We confirmed that, despite certain difficult issues and complications, we nevertheless agree with these proposals and are ready to show the flexibility that has been offered to us,” Putin said.

 But he claimed since the summit that the Trump administration had paused and claimed that was because Ukraine is unwilling to accept the plan.

 “I believe the reason is the same: the US administration has not yet managed to secure the agreement of the Ukrainian side, as Ukraine is opposed to it. Apparently, Ukraine and its European allies are still under the illusion that they can inflict a strategic defeat on Russia on the battlefield,” Putin said.

The Russian leader vowed that if Ukraine did not discuss the proposals, Russia would continue to attempt to seize more cities and achieve its goals via force.

 Zelenskyy on Friday warned Putin would attempt to use the peace talks to try to frame Ukraine as unwilling to accept peace, while making unjust demands.

“There will be a constructive search for solutions” with the U.S., he said. “I will present arguments, I will persuade, I will offer alternatives, but we will certainly not give the enemy any reason to say that Ukraine does not want peace, that it is Ukraine who disrupts the process and is not ready for diplomacy. That will not happen.”

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