Above the North Pole, in an atmosphere that receives little attention and is even less understood, a transformation is underway. Over the next 10 days, changes in the stratosphere will significantly alter weather patterns, ushering in a cold and snowy December for some parts of the Northern Hemisphere.
This means a dramatic change in weather for some parts of the United States, which are currently smoldering with record heat just one week before Thanksgiving.
This may also be one of the earliest significant polar vortex disruptions recorded since the dawn of the satellite era.
Think of the stratospheric polar vortex like a wall of wind that corrals the frigid arctic air above the North Pole. When the cold air weakens, it will flow from the south into 48 degrees north latitude, Europe, and Asia.
Currently, the air in the stratosphere (the layer of the atmosphere above where most weather occurs) is rapidly and dramatically warming, a phenomenon known as sudden stratospheric warming.
But the sudden warming of the far upper atmosphere will bring nothing but warmth. This could weaken the polar vortex winds and even cause them to flow in reverse, said Amy H. Butler, a meteorologist with the National Oceanic and Atmospheric Administration.
Scientists are still working to figure out why these warming events occur and whether there are good reasons for it. That means it could trigger the most intense “polar vortex” cold outbreak in the United States.
Over the next two weeks, these changes could begin to be felt across North America, Europe, and Asia. The polar vortex weakens, causing the top to slow down and roll south off course.
One unusual feature of this event is its timing. Judah Cohen, a meteorologist and researcher at the Massachusetts Institute of Technology (MIT), said a sudden stratospheric warming event of this magnitude is almost unprecedented in November.
Although it is not yet certain whether a major winter explosion will occur, scientists are watching for colder-than-normal conditions to occur over the next month or so in mid-latitude regions, where most of the world’s population lives. Once the polar vortex is disrupted, it can take more than a month to recover, said Andrea López Lang, a meteorologist at the University of Wisconsin-Madison.
The hardest thing to predict is where the polar vortex will cause ice explosions, but the temperature outlook still doesn’t fully take that into account.
“Regions across the Northern Hemisphere are seeing more active and altered storm trajectories and increased occurrence of cold air,” she said in an email.
Butler and López-Lang said that accurate predictions of polar vortex events could make seven- to 10-day forecasts more accurate, which could be useful for decision-making.
“The stratospheric polar vortex lies several miles above us, but it can be connected to the weather through invisible puppets explained by atmospheric mechanics and thermodynamics,” López-Lang said.
For example, the United States experienced a cold and snowy December after other polar vortex events occurred earlier in the winter, she said. Such polar vortex events tend to create a warm, high-pressure ridge over Alaska, which causes a depression, or trough, in the eastern jet stream. The trough could bring colder, snowier weather to the central states and parts of the eastern United States.
López-Lang said that while these polar vortex events are shocking, scientists are losing sight of this layer of the atmosphere.
Satellites are essential for observing the stratosphere and predicting sudden stratospheric warming events, he said, and some of that data will disappear as the satellites age and NOAA makes budget and program decisions that will affect the availability of current and future measurements. She cited some newly lost data from polar-orbiting satellites as an example.
“The only way to actually observe these phenomena is through satellite data,” she said.
