U.S. a winter wild card as vortex splits

A dramatic spike in temperatures is occurring at high altitudes above the North Pole, where the air is thin and typically frigid. Known as a sudden stratospheric warming event, experts say it’s likely to have potentially significant repercussions for winter weather across the Northern Hemisphere for weeks to possibly months.

This unusually strong event may have profound influences on the weather in the United States and Europe, possibly increasing the potential for paralyzing snowstorms and punishing blasts of Arctic air, with the odds of the most severe cold outbreaks highest in Northern Europe. The United States is slightly more of a winter wild card for now, experts say, with individual winter storms tough to predict beyond a few days in advance.

While occurring about 18 miles high in the sky and disconnected from the weather on the ground, stratospheric warming events can affect the polar vortex, which is a circulation of air around low pressure that acts as a repository for some of the coldest air on the planet.

If the polar vortex is strong and stable, as it was last winter, that cold air will stay bottled up over the Arctic, and snow chances may be few and far between for regions such as the Mid-atlantic and Northeast.

But when the polar vortex weakens and wobbles off the pole, pieces of it can swirl southward, affecting the United States, Europe and Asia. And that’s exactly what’s begun to happen, due in large part to this stratospheric temperature spike.

••• To accurately forecast how winter weather may soon unfold in the United States and elsewhere, seasonal forecasters like Judah Cohen of Atmospheric and Environmental Research in Massachusetts are trying to figure out how the events in the stratosphere will ripple back downward into the troposphere, the layer of the atmosphere where most weather occurs.

Stratospheric warming events are a known, but not guaranteed, trigger for knocking the polar vortex off balance, like flicking a spinning top, forcing it to spin more slowly and erratically. They are triggered by an upward flow of energy in the form of “large-scale atmospheric waves” from the lower atmosphere, according to Amy Butler, a research scientist at the National Oceanic and Atmospheric Administration’s Chemical Sciences Laboratory.

Now, the stratosphere stands poised to transfer energy via downward-moving atmospheric waves into the lower atmosphere, where it can help determine which areas get buried in blizzards while others see unusually mild conditions.

Normally, winds in the stratosphere circulate from west to east around the North Pole, around an area of low pressure. But the rapid warming — on the order of 86 degrees Fahrenheit in the past two weeks — taking place in the frigid, darkened Arctic is causing that low-pressure area to break down and the winds to slacken, Butler says. The winds are even poised to reverse, which can increase the chances of stratospheric weather affecting conditions in the lower atmosphere.

The polar vortex is synonymous with extreme cold and snow. Pieces of the vortex broke off and swirled southward during the infamous winter of 2013-14, when Chicago turned into “Chiberia” and heavy snow fell from Washington to Boston. Similar events occurred during the winter of 2009-10, which was D.C.’S snowiest on record.

So the news that the bone-chilling lobes of ultracold air may soon be on the march again may be cause for concern for anyone worried about a harsh winter in the United States and Europe in particular. This is especially the case this year given the challenges posed by the ongoing pandemic and demonstrated ability of the coronavirus to spread readily in indoor settings.

The United States is slightly more of a winter wild card for now, experts say, with individual winter storms tough to predict beyond a few days in

advance.