When Chicago and the Midwest became snow-clogged, Hoth-like hellscapes last winter, media outlets found and clung to a term most people in the United States had never heard before: polar vortex.
Today, multiple articles are one again name-dropping polar vortex, as severe wintery storms sweep across much of the United States this week. But some experts that spoke with VICE News have outright rejected characterizing this storm as a polar vortex.
So what gives?
"The polar vortex has been around forever, but the media only noticed it last year," Jeff Masters, Director of Meteorology at Weather Underground told VICE News. "And it's really not worth drawing attention to. It's not like the entire vortex has shifted southwest over the US. So it's kind of a misconception of what the term polar vortex implies."
The polar vortex is a wind pattern that circles the North Pole, looping around it from west to east, and corralling cold air. Much of that air is concentrated in the upper part of the atmosphere and can be thought of as something akin to a spinning wheel. Sometimes, like last year, the swirling air breaks into smaller wheels that are pulled south, bringing frigid temperatures along with them.
"What happens is this spinning vortex of air has bulges in it, called troughs of low-pressure and regions of high pressure," Masters said. "It's not a perfectly circular vortex, it's got little lobes. What happened is last year, one of these lobes of the polar vortex went over the eastern US — and there's one going over the upper-Midwest right now — and when that happened, it means that cold air from the Arctic spilled southwards to where this bulge is."
This week we're getting a taste of that little lobe, linked to the polar vortex, says Masters. Masters is one voice in a discussion among scientists about exactly when to use the polar vortex terminology, because the southward trough hitting the US right now is not a fully broken part of the polar vortex.
"There's nothing mysterious about this," Mark Serreze, director at the National Snow and Ice Data Center and professor in the geography department at the University of Colorado Boulder told VICE News.
"All the polar vortex is, is the region of cold air in the northern hemisphere, separated from the warmer air to the south by what we call the polar front jet stream," he explained.
As the quickly moving air in the polar front jet stream descends into lower latitudes, it brings along cold and stormy weather in low pressure systems. A big storm or a series of big storms can change the southern boundaries of the vortex, pushing and pulling the jet stream. Storms often develop below this front jet stream boundary of the polar vortex.
Serreze speculates that this particular cold snap is likely the result of Typhoon Nuri that hit Alaska last week. He added that some research has linked a warming Arctic and the loss of sea ice cover to potential permanent changes in the polar vortex.
So the snowy storms trekking their way across the US are nothing new. Southward troughs, or the changing jet stream boundary beneath the polar vortex, have always caused stormy weather in late fall and winter.
And because wintery weather occurs along the low-pressure polar front during a trough's southward push, some media want to use the term polar to describe what's happening. The reality is more complicated: the weather this week is linked to but not exactly a reeling, broken-off piece of the polar vortex.
Despite the error of using the headline grabbing term, the storm remains noteworthy in its ferocity.
"I'm struggling to think of a time when we've dropped more than 40 degrees in five hours, which is what we've done in Denver today," Josh Larson, a meteorologist at Weather5280, told VICE News.
"What's really causing this cold weather is an unusually strong ridge of high pressure over Alaska, and that's just allowing the Arctic air to flow into the continental U.S.," he said. "That's creating a downstream trough and that's really almost acting as a conveyor belt for the cold air."
So when cold weather hits this week, remember that it's just that time of year, and cold weather sweeps in for a whole lot of reasons, not just because of the over-hyped polar vortex.
Follow Shelby Kinney-Lang on Twitter: @ShelbKL