High above the North Pole, in a largely overlooked part of the atmosphere, a big shift is forming. Over the next 10 days, developments in the stratosphere are expected to change global weather patterns and could pave the way for a colder and snowier December across parts of the Northern Hemisphere.
Several parts of the United States currently enduring record heat just days before Thanksgiving could soon see a dramatic reversal. Scientists say it could be one of the first significant disruptions to the polar vortex since satellites began tracking it.
Think of the stratospheric polar vortex as a fast-moving ring of wind that keeps cold arctic air contained at the top of the world. As this ring weakens, icy air can sink into areas such as the Lower 48, Europe, and Asia.
Currently, temperatures high in the stratosphere — above the layer where daily weather is formed — are rising sharply during a phenomenon known as sudden stratospheric warming. Despite the name, the effect on the surface is often the opposite. Amy H. Butler, a meteorologist with the National Oceanic and Atmospheric Administration, told CNN that warming in the air is weakening the polar vortex and its winds could even reverse.
Researchers still don’t fully understand why these episodes occur, but they know the consequences can be serious: they often precede the strongest “polar vortex” cold outbreaks in the United States.
Over the next fortnight, impacts may begin to appear across North America, Europe and Asia as the disturbed vortex moves south like a spinning top losing its balance. Judah Cohen, a scientist at MIT, notes that an event of this magnitude is highly unusual in November.
Are you in for a big winter blast?
While a major winter outbreak isn’t guaranteed, forecasters are watching for below-average temperatures in the mid-latitudes over the next month. Once a vortex is disrupted, it can take weeks to recover, said Andrea Lopez Lang of the University of Wisconsin-Madison. It remains uncertain which areas will feel the brunt of the cold, and long-term temperature outlooks do not yet fully reflect these developments.
Why is the polar vortex important?
The polar vortex strongly influences winter conditions in the Northern Hemisphere. If it stays solid, it will keep the cold over the Arctic. When it falters, the cold can spill south — much like opening a freezer door — and bring colder and snowier weather than usual.
