A polar vortex disruption is on the way, and its magnitude is almost unheard of in November
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 shake up weather patterns and set the stage for a cold and snowy December in parts of the Northern Hemisphere.
This will mean a drastic change in the weather in parts of the United States currently experiencing record heat, and it could start the week of Thanksgiving.
It could also be one of the first significant disruptions of the polar vortex recorded since the dawn of the satellite age.
Think of the stratospheric polar vortex as a wall of wind, gathering ultracold arctic air above the North Pole. When it weakens, cold air spreads southward to places like the Lower 48, Europe, and Asia.
Currently, the air in the stratosphere – the layer of the atmosphere above which most weather occurs – is warming rapidly and significantly, in a phenomenon known as a sudden stratospheric warming event.
But the sudden warming in the upper layers of the atmosphere will produce nothing but heat. This causes the polar vortex winds to weaken, said Amy H. Butler, a meteorologist with the National Oceanic and Atmospheric Administration, and they could even reverse.
Scientists are still trying to understand why these warming phenomena are happening, and for good reason: They can trigger the most intense “polar vortex” cold air outbreaks in the United States.
Over the next two weeks, these changes could begin to be felt across North America, Europe and Asia, as the polar vortex weakens and tumbles southward, like a top that slows and wobbles.
An 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 researcher at MIT.
It is not yet certain whether there will be a major winter storm, but scientists expect colder-than-normal conditions to develop in the mid-latitudes – where most of the world’s population resides – over the coming months. Once the polar vortex is disrupted, recovery can take a month or more, said Andrea Lopez Lang, a meteorologist at the University of Wisconsin-Madison.
What’s hardest to predict is where the polar vortex will produce its icy blast, and temperature forecasts don’t yet fully account for this.
“We may see more active, shifted storm tracks and increased cold air outbreaks across regions of the Northern Hemisphere,” she said in an email.
Butler and Lopez Lang said having accurate forecasts for polar vortex events can help improve 7- to 10-day forecasts, which can be beneficial for decision-making.
“Even though the stratospheric polar vortex is miles above us, it is sometimes connected to our weather via invisible puppet strings that we describe with atmospheric dynamics and thermodynamics,” Lopez Lang said.
For example, other polar vortex events in early winter were followed by colder, snowier Decembers in the United States, she said. Polar vortex events like these tend to generate a warm ridge of high pressure over Alaska, which triggers a trough, or trough, in the jet stream to the east. This trough could bring colder and snowier weather to the central states and parts of the eastern United States.
As impactful as these polar vortex events are, scientists are losing part of their eyes on this layer of the atmosphere, Lopez Lang said.
Satellites are essential for observing the stratosphere and making predictions about sudden stratospheric warming events, she said, and some of that data disappears as satellites age and NOAA makes budgetary and programmatic decisions that affect the availability of current and future measurements. She cited some recently missing data from polar-orbiting satellites as an example.
“The only way to actually observe these phenomena is through satellite data,” she said.
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