High above the North Pole, in a slice of atmosphere rarely noticed and even less understood, a transformation is underway. Over the next 10 days, changes in the stratosphere will upend weather patterns and set the stage for a cold, snowy December across parts of the Northern Hemisphere.It will mean a dramatic swing in weather for parts of the US that are currently simmering in record heat, and it could begin the week of Thanksgiving.It could also be one of the earliest significant polar vortex disruptions recorded since the dawn of the satellite era.AdvertisementAdvertisementAdvertisementAdvertisementThink of the stratospheric polar vortex like a wall of wind, corralling the ultra-cold, Arctic air over the North Pole. When it weakens, cold air spills south into places like the Lower 48, Europe and Asia.Right now, the air in the stratosphere — the layer of the atmosphere above where most weather occurs — is warming quickly and dramatically, in a phenomenon known as a sudden stratospheric warming event.But the sudden warming in the far upper atmosphere is going to result in anything but warmth. It is causing the polar vortex winds to weaken, said Amy H. Butler, a meteorologist at the National Oceanic and Atmospheric Administration, and they could even reverse.Scientists are still trying to figure out why these warming events happen, and for good reason: they can trigger the most intense “polar vortex” cold-air outbreaks in the US.AdvertisementAdvertisementAdvertisementAdvertisementOver the next two weeks, these shifts could start to be felt in North America, Europe and Asia as the polar vortex weakens and tumbles south, like a spinning top that slows and wobbles off course.One unusual feature of this event is its timing; sudden stratospheric warming events of this magnitude are almost unheard of in November, said meteorologist Judah Cohen, a research scientist at MIT.It’s still not certain there will be a major winter blast, but scientists are watching for colder than normal conditions to develop in the mid-latitudes — where most of the world’s population resides — over the next month or so. Once the polar vortex is disrupted, it can take a month or more to recover, said Andrea Lopez Lang, a meteorologist at the University of Wisconsin-Madison.What’s most difficult to predict is where the polar vortex will deliver its icy blast, and the temperature outlooks aren’t taking it fully into account, yet.AdvertisementAdvertisementAdvertisementAdvertisement“We can see more active and shifted storm tracks and increases in cold air outbreaks in regions across the Northern Hemisphere,” she said in an email.More in ScienceBoth Butler and Lopez Lang said having accurate forecasts for polar vortex events can help make 7- to 10-day forecasts better, which can b …
