This week’s weird, lethal climate—snow on the Mexican border, ice-locked roads in Louisiana, and subzero temperatures in central Texas—all begins within the Arctic, the place a barrier that usually retains out polar winds has switched sides.
Under regular circumstances, the jet stream (a band of fast-moving wind that encircles the North Pole) herds the freezing arctic air, retaining it largely contained over the Pole. But the jet stream isn’t completely spherical: it strikes in a free wave at excessive latitudes. Oftentimes, that wave crests over Alaska, and drops down over the Great Plains, or vice versa.
Right now, the jet stream has bulged down to this point that it loops round almost all the continental US, letting supercooled polar air pour throughout the Great Plains, in what’s referred to as an “arctic outbreak.”
The bulge was kicked off by a zone of excessive strain that shaped over Alaska in January, and diverted the jet stream to the south. Under regular circumstances, that loop would have began transferring to the east, relieving the midwest of chilly temperatures, says Brad Pugh, a meteorologist with the National Oceanographic and Atmospheric Administration’s Climate Prediction Center.
But this 12 months, he says “there’s also been a strong area of high pressure over the Southwest Atlantic, just offshore the southeastern US.” The two excessive strain zones have pinned the jet stream in place, retaining the Great Plains within the bull’s eye.
By the center of subsequent week, he says, “temperatures will either be near or above normal across the Great Plains,” with highs within the 60s in Texas. But the length of this explicit arctic outbreak is, to his data, “unheard of.”
Part of the present stickiness of the jet stream may very well be associated to a breakdown of the high-altitude polar vortex earlier this winter, says Amy Butler, an atmospheric scientist at NOAA’s Chemical Sciences Laboratory. The polar vortex is a zone of chilly air that usually spins like a high excessive above the North Pole. But when it’s disrupted, “air pressure builds up over the Arctic, displacing the Arctic air south,” Butler says, though she cautions that the precise relationship between the jet stream and the vortex are nonetheless unknown.
Also driving the severity of the outbreak, says Mark Seeley, a longtime climatologist with the University of Minnesota, is that air over the Arctic has sat in place for months. “In those seasons of long nights and short days, [the air] just incubates and gets denser and colder, and denser and colder.”
Then, when the jet stream buckles over the central US, that dense, chilly air plows south. “[The Arctic air] is so massive, and so amplified in terms of cold,” says Seeley, “that it just runs over everything and sets all kinds of cold temperature records.”
Outbreaks of this scale solely occur each few generations, says Seeley, however they aren’t essentially unprecedented. In 1899, an arctic outbreak led to subzero temperatures in Tallahassee, Florida. On February 17 of that 12 months, individuals in New Orleans watched chunks of ice float down the Mississippi on their approach to the Gulf of Mexico, the place an inch-thick layer of sea ice had shaped.
“People who have lived through these remember them the rest of their lives,” Seeley says, “but they just have a single episode to remember.”
According to Butler, the connection to climate change remains unclear. Some local weather fashions recommend that because the Arctic warms, the jet stream will change into wavier, and due to this fact extra prone to let polar air spill into arctic outbreaks. But different researchers argue that fashions have proven combined outcomes, typically even discovering a strengthened, extra secure jet stream.
But even when these sorts of disruptions change into extra widespread, Butler says, deep freezes are nonetheless going to be rarer.
“The overwhelming response to climate change will be that things will get warmer everywhere,” she says. Even if outbreaks of polar air change into extra widespread, “what’s ‘cold’ in 2080 could be a really warm day in today’s climate.”