Disrupted polar vortex unleashing colder weather in eastern U.S.

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COMMENTARY

In mid-February, air temperatures 10 to 30 miles above the North Pole rose to 50 degrees, setting in motion a chain reaction process that is already affecting North American weather. Known as a “sudden stratospheric warming” event, the sudden warming of the stratosphere – the second layer of the Earth’s atmosphere – disrupted the polar vortex and led to its destruction.

Since that episode three weeks ago, dominoes have fallen that have changed weather patterns in North America. Now, it looks like parts of the eastern United States — which have so far been spared the wrath of Old Man Winter — could face a cold spell and an increased chance of winter storms.

Already, the development of high pressure over Greenland—a textural response to polar vortex disruptions—is helping to shift cold air from the Arctic and transplant it south. The Arctic has turned suddenly mild in many areas, while below-average temperatures are reaching the eastern United States, all as a pair of winter storms prepare to march from the Upper Midwest into the interior Northeast and mid-Atlantic.

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It comes as the calendar inches ever closer to astronomical spring, but winter may not be quite ready to relinquish its grip just yet. Experts believe the disruption of the polar vortex is already having an impact – and the last hurricane of winter could be in sight.

What happened to the polar vortex?

The stratospheric polar vortex is like a severe atmospheric vortex located at two or three times the altitude that commercial airliners fly. Cold temperatures over the North Pole, caused by a lack of sunlight, cause the air columns to become denser and contract towards the ground. This creates a kind of void in the upper atmosphere, which causes an internal vacuum-like effect. As the surrounding air rotates counterclockwise in the vortex, it also cools, repeating the same process.

The stronger the vortex, the faster it spins. This keeps the Arctic bottled cold at high latitudes. But if something happens that weakens the vortex or disrupts its circulation, then lobes of bone-chilling air can descend toward the midlatitudes.

It takes weeks, but after any disruption of the polar vortex or sudden stratospheric warming event, impacts can begin to show in the lower atmosphere.

“It’s very typical there [is] a long delay between its onset and the maximum visible impact on the weather,” Simon Lee, an atmospheric scientist at Columbia University, wrote in an email.

Lee said the sudden stratospheric warming came in two streams — an initial shift in the winds of the stratospheric polar vortex on February 16, and then a doubling of that vortex weakening at the end of the month.

“[The Feb. 16 event] at first it was too short and too high to have much impact, but once this was amplified, things changed,” Lee wrote.

This is why only now are the effects fully realized.

Researchers point to several telltale signs that sudden stratospheric warming is starting to shape midlatitude weather patterns.

First, the weakening of the polar vortex helped turn the AO, or Arctic Oscillation, into a negative state. When the AO is positive, cold air tends to bottle up over the Arctic as the polar vortex is strong and stable. But when the AO swings negatively, it signals that the vortex has been disturbed and the doors are open for Arctic air to flow south.

Judah Cohen, an atmospheric scientist with Atmospheric and Environmental Research, likened the polar vortex’s patchy impact on midlatitude weather to “dripping paint,” with each dot marking the onset of cold air and possible wintry weather. He says one of them is already affecting northeastern North America, and wrote in a direct message on Twitter that models “also show another impact or drop in about a week, [suggesting] there may be more.”

Second, a “Greenland block” has been created. One of the symptoms of a classic sudden stratospheric warming event is often the emplacement of this block, which is a stagnant dome of high pressure near Greenland. It diverts the jet stream south into eastern North America, allowing cold air from the Arctic to flow south.

Although much of the eastern United States has seen record warmth since the December holidays, colder weather has begun to descend. In the next six to 10 days, the National Weather Service’s Climate Prediction Center is highlighting a “very likely” easterly. of below-average temperatures and calls for cooler-than-average weather through early April.

Additionally, the presence of a stalled high pressure system may induce some sort of atmospheric blockage, maintaining an above-average period of storminess over the East Coast. While that has yet to happen, signs point to an unsettled stretch in the next one to two weeks. Forecast models show the potential for a mix of rain and snow from successive storm systems late this week and early next week across parts of the mid-Atlantic and Northeast.

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In a phone call, Cohen explained that the effects of the vortex disruption probably began at least a week ago.

“I think we’ve already seen the impacts,” he said. “We had a low level of closure [pressure system] over western Russia and eastern Europe. It was kind of cold and snowy there. We also saw a closed low that tried to develop in the Canadian Maritimes. Boston, New York and DC haven’t seen much snow, but New England ski resorts have.”

He attributed some of the northern New England snow to a sudden shake-up in late February after the actual breakup of the polar vortex itself.

“Portland, Maine, is practically back to normal [snowfall] for the season”, he said. “I think this was a faster impact from the polar vortex disruption.”

That said, one thing certainly works against the chances of snowfall, much to the chagrin of winter lovers – the weather. The days are getting longer, the angle of the sun is increasing, and whispers of spring are beginning to creep into the atmosphere.

“The clock is definitely about to strike midnight,” Cohen said. “After a week or two, the impact of the polar vortex may fade or disappear … but that’s still a question mark.”