What is the polar vortex and how could its early disruption impact the US this winter?

A disruption of the polar vortex over the Arctic has put a question mark on what kind of winter weather the United States could experience in the coming weeks. The phenomenon, which normally strengthens as winter approaches, is weakening unusually early this year.

According to a report by Newsweek, the chilly winds high above the Arctic dropped to 9 mph on November 3, compared with an average of 58 mph and a previous record low of 32 mph for the date, citing AccuWeather. However, as per forecasters, this will not trigger a major Arctic cold outbreak across the US.

“The polar vortex is weakening at a time when it should be gathering strength, but a key ingredient for a significant Arctic blast in the United States is missing. There simply has not been enough cold air building across Canada to send south,” Newsweek quoted AccuWeather meteorologist Tyler Roys.


So, what exactly is the polar vortex, why is its early disruption unusual, and could it bring freezing temperatures to parts of the US?

What is the polar vortex?

The polar vortex is a large area of low pressure and extremely cold air that surrounds both of Earth's poles. It is a permanent atmospheric feature that always existed, which, as per the National Weather Service(NWS), “weakens in summer and strengthens in winter.”

The term “vortex” refers to the counter-clockwise flow of air that helps keep colder air near the poles. The NWS explains that the polar vortex is not a new phenomenon and does not exist at Earth's surface.

“Weather forecasters examine the polar vortex by looking at conditions tens of thousands of feet up in the atmosphere,” the agency said; however, when extremely cold air from the Arctic regions reaches Earth’s surface, sometimes it is associated with the polar vortex.

During the Northern Hemisphere's winter, the polar vortex can expand or weaken, which lets the cold Arctic air move southward with the jet stream. This is the reason people across the United States, as well as parts of Europe and Asia, experience unusually low temperatures.

The NWS notes that similar cold-air outbreaks have occurred in several previous winters, including 1977, 1982, 1985, 1989 and January 2014.

Why is the polar vortex weakening unusually early?

The polar vortex generally strengthens as temperatures fall over the Arctic during the transition into winter. However, the current disruption is happening at a time when the system would normally be gathering strength.

According to Newsweek, AccuWeather meteorologist Lydia Burroughs described the unusual atmospheric pattern, saying, “While some amount of disruption to the polar jet is pretty typical for fall as the transition to winter begins, the current polar jet pattern appears more like it's midwinter than midfall.”

One of the major factors influencing the potential impact of the polar vortex on the United States is the temperature pattern across Canada. “The largest factor preventing a major Arctic outbreak in the United States is the warmth that remains to the north in Canada. Not only is it early in the cool season, but persistent high pressure has kept temperatures in the territories and northern prairie provinces 10-20F above the historical average. This is the air the polar jet brings with it when it dips into the central and eastern U.S. Until these areas become cooler, that air will feel more like fall than the Arctic,” the meteorologist told Newsweek.

Meanwhile, much of the coldest air is currently concentrated over northern Russia. This means a shift in the atmospheric pattern could have a greater impact on parts of Europe and Asia than on the United States.

How could an early polar vortex disruption impact the US?

In the current situation, AccuWeather does not expect the early disruption to produce a major Arctic outbreak across the United States. “This is an extraordinary atmospheric event, but it may end up having very little impact on weather in the United States,” Roys told Newsweek.

And according to forecasters, it is the southwestern states that will see some of the sharpest drops in temperature. Temperatures could still become cooler in some parts of the country during November, but it will be due largely to local weather patterns rather than the polar vortex itself. AccuWeather also expects the possibility of chillier air moving south later in November and into December.