The Polar Vortex Will Weaken Much Earlier Than Usual; Here’s What That Could Mean In December

The polar vortex is expected to weaken unusually early, which could lead to more persistent cold weather in at least parts of the United States in December.

Last week, nearly 100-day record lows were tied or broken in the East and South; these include records for the “coldest at the beginning of the season”. The cold quickly retreated from most areas.

However, there are hints that cold may prevail in the atmosphere, at least for a while.

What is polar vortex: Almost 12 years ago, the “polar vortex” entered popular culture during the January 2014 cold outbreak. But scientists have known this for many years, even before the Civil War.

Located near the poles (hence the “pole”), this low-pressure rotating cone (a vortex) is always there during the cold months. But it’s in the stratosphere, the layer of atmosphere above which most weather occurs, about 7 to 31 miles above the Earth’s surface.

Sometimes it is a perfect cone: The strength, shape and location of this polar vortex may vary during the colder months.

Sometimes it is powerful, almost perfectly circular and directly above the pole.

Other times not so much: But from time to time, the polar vortex weakens, lengthens, and even splits into two, being pushed out of the central pole.

This is usually caused by sudden stratospheric warming (SSW). By suddenly we mean that temperatures in the stratosphere could rise 50 to 70 degrees or more in just a few days.

While this may seem like an extreme situation, experts say it usually happens at least once every cold season. data Compiled by NOAA scientist Amy Butler.

Strange early weight loss prediction: And that’s what’s expected to happen soon. As you can see in the graph below, the polar vortex is expected to be pushed away from the North Pole by the influence of warm air, possibly towards the end of November, stretching like both ends of a rubber band are pulled.

If warming in the stratosphere is strong enough to divert typical westerly winds to the east, this is called major sudden stratospheric warming.

Inside records Before this event, which dates back to the late 1950s, there had been a major GGB event only twice, in 1968 and 1958, in the short period of November. And the last time it occurred was in December 1998. So this could be the earliest such event in at least 27 years.

Why all this matters: Cold air can and does move into the US and Europe without sobs in the polar vortex.

Although not always, changes in the polar vortex can gradually trickle or leak downwards and eventually affect the jet stream pattern that drives our weather. However, the effect is exactly the opposite of what you think.

When the polar vortex is strongest, circular, and centered near the North Pole (as shown in the previous image), you’re less likely to see cold air plunge deep into North America or Europe. This stronger polar vortex effectively helps seal in cold arctic air from the mid-latitudes.

When the polar vortex weakens, as predicted for late November or December, blocking patterns It may eventually become established at higher latitudes, affecting the persistence of cold air masses.

Decemberrrrr: Despite this general scenario, forward predictions for December may be misleading.

“This appears to be a long-lasting event and I expect weather models to have difficulty accurately simulating how the event develops and how it will affect our weather.” Judas CohenMIT research scientist and director of seasonal forecasting at Atmospheric and Environmental Research told weather.com.

This polar vortex weakening could increase the risk of severe winter weather over an extended period of time, Cohen said.

“The key to weather impacts in the U.S. is that the SSW event should result in altering the Pacific jet stream,” said the University of Oklahoma associate professor. Jason Furtado “…and that takes time,” he told weather.com in a 2019 interview.

“There is generally a 2 to 4 week delay (after the polar vortex weakens) in impacts to the U.S., especially the central and eastern U.S.,” Furtado said.

This is just one factor, along with La Niña, in the outlook for an overall cooler December for the northern tier, as you can see below.

It also remains unclear how long this cold weather will last into December or the rest of the winter.

According to Atmospheric G2 Vice President of Meteorology Todd Crawford, previous January through March periods following the SSW showed a cold trend in the West and Plains, but were milder in the Great Lakes and Northeast.

So, enjoy the lighter spells in the northern tier of the US while you can. This situation may change rapidly in December.

(MORE: Winter View)

Jonathan Erdman is a senior meteorologist at weather.com and has been covering national and international weather since 1996. Extreme and strange weather conditions are his favorite subjects. Contact him blue sky, X (formerly Twitter) And Facebook.