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Discover your lengthy johns, escape the thick socks and raid the grocery store. After a month of comparatively delicate winter climate, the Midwest and the East Coast are bracing for what’s changing into a seasonal proper of passage: the polar vortex.
The phrase has change into synonymous with frigid temperatures that make snowstorms extra probably. A blast of arctic air is anticipated to herald the vortex’s arrival on Monday.
If it appears as if these polar freezes are taking place extra usually, you’re proper. “They’re undoubtedly changing into extra widespread,” mentioned Jennifer Francis, a senior scientist on the Woods Gap Analysis Middle. “There have been a few research which have documented that.”
The chilly snap could really feel particularly surprising after an unusually heat few weeks. Colder temperatures have been arriving later in winter over the previous few years, in response to Judah Cohen, a climatologist at Atmospheric and Environmental Analysis, a climate danger evaluation agency. However due to modifications to the polar vortex, when wintry climate does arrive, it’s usually extra intense — witness the 4 back-to-back nor’easters final yr.
“I’ve been making that argument that winter is shortening, however you’re getting these extra intensive intervals in that shorter winter,” Dr. Cohen mentioned.
A serious snowstorm has already pummeled elements of California and is heading east, blanketing the Plains with blizzardlike situations. Over the weekend, snow is anticipated throughout the Midwest, the East Coast and as far south as Arkansas. However as soon as the storm clears out, the results of a dipping polar vortex will arrive. Monday’s excessive temperature in New York Metropolis is predicted to succeed in simply 16 levels, 20 levels beneath common, in response to the forecasting service Climate Underground.
“We’re going into what seems like a reasonably unusually chilly interval, even for late January, punctuated by some winter storms,” mentioned Bob Henson, a meteorologist with Climate Underground.
Scientists are nonetheless making an attempt to determine why these intense arctic chills are flooding southward extra regularly. To know their considering, it helps to know the character of the polar vortex. Whereas the expression turned broadly standard throughout an unusually chilly winter in 2014, the vortex was identified to meteorologists lengthy earlier than that.
The time period refers to round bands of winds close to the poles which are strongest in wintertime and effectively above the jet stream within the stratosphere. The stratosphere is an atmospheric layer that extends roughly seven to 31 miles above the earth.
Normally, these round bands act as partitions that hold the teeth-chattering chilly air locked on the poles. However, now and again, the winds break down and permit the chilly air to flee. That’s what occurred originally of this month, when the polar vortex cut up into three separate bands.
It’s this escaping polar air that’s dropping temperatures within the Midwest and the East — there’s a lag time between the atmospheric occasion and once we expertise the results. The damaged vortex can be sending icy temperatures to a lot of Europe in what some name the “Beast From the East.”
Some researchers, together with Dr. Francis and Dr. Cohen, say they believe that the extra frequent polar vortex breakdowns might be tied to local weather change.
Whereas local weather change is warming the earth, not all elements of the earth are warming on the identical fee; the Arctic is warming at a fee twice as quick because the world common. That warming has led to historically low levels of sea ice in the region. The melting sea ice, particularly in an area near the Barents and Kara Seas off Siberia, may be linked to the changes in the polar vortex.
“When we lose a lot of ice in that particular area in the summer, it absorbs a lot of extra heat from the sun,” Dr. Francis said. This is because the darker open ocean absorbs more heat than reflective ice. “And so we see a very persistent, hot spot there in terms of temperature differences from what they should be.”
Research suggests that the hot spot, along with changes in the jet stream driven by climate change, cause the polar vortex to break down in mid- to late winter.
“As the Arctic gets warmer and warmer, the severe weather picks up,” Dr. Cohen said.
Whether the polar vortex directly caused the snowstorm is a tricky question, Mr. Henson said. There have always been major winter storms, of course. In this case, the polar vortex, the El Niño pattern and the jet stream flowing from the Pacific all play a role, he said.
In October, the National Oceanic and Atmospheric Administration predicted a milder than average winter, but that is not necessarily at odds with the coming chill.
“There’s a difference between some seasonal outlooks such as NOAA’s that look at the whole three-month period and others that may be breaking it down month by month,” Mr. Henson said. “It’s quite possible the winter will average warm for December through February. But that may well manifest as the extreme warmth we’ve seen over the last month followed by some much colder and colder than average conditions into February.”
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