RACHEL MARTIN, HOST:
Much of the country had to bundle up this past week due to some unusually cold weather. Even in the Deep South, residents struggled with temperatures in the low 20s. With a big chill comes the revival of that ominous sounding phrase - the polar vortex. Michell Eloy from member Station WABE in Atlanta reports.
MICHELL ELOY, BYLINE: Lately, it's been hard to escape the phrase.
(SOUNDBITE OF VARIOUS NEWS REPORTS)
UNIDENTIFIED REPORTER #1: The return of the polar vortex.
UNIDENTIFIED REPORTER #2: A dreaded return of the polar vortex.
UNIDENTIFIED REPORTER #3: New polar vortex could put the squeeze on holiday shopping.
UNIDENTIFIED REPORTER #4: Chicago is already storing salt like a squirrel stores nuts.
ELOY: "The Today Show" used it in promos this past week.
(SOUNDBITE OF "THE TODAY SHOW" PROMO)
UNIDENTIFIED ANNOUNCER: You've got to face the polar vortex.
ELOY: And "The Tonight Show's" Jimmy Fallon poked fun at the hype.
(SOUNDBITE OF TV SHOW, "THE TONIGHT SHOW")
JIMMY FALLON: Pro, it's a phenomenon that signals the return to colder temperatures across North America. Con is it used to be called the month of November.
ELOY: And that's exactly what Jeff Masters wants people to understand.
JEFF MASTERS: This is just a regular old cold front.
ELOY: Masters is chief meteorologist at weatherunderground.com. He says the recent popularity of the phrase is misleading.
MASTERS: The polar vortex has been around forever. And it's just the media happened to notice it last year. And it's really not a very scientifically accurate thing to talk about saying, you know, we're getting the polar vortex.
ELOY: And in fact, some Atlantans who braved the cold had heard the phrase, but weren't really sure what it meant.
JANET CROSS: Does is have something to do with the large ice caps that are melting?
VIVIAN COOK: The poles are vortexing.
LAURA REECE: Cold wind blows off the North and South Poles and circulates around. I don't really know.
ELOY: That's Janet Cross, Vivian Cook and Laura Reece. So here's what the polar vortex really is. It's a constant flow of arctic air circling in the upper atmosphere above the North and South Poles. The cold is usually corralled up there. But sometimes little bits of the Arctic air escape. Again, Weather Underground's Jeff Masters.
MASTERS: It's just the ordinary sort of weather you expect in winter. Every now and then, you get a trough of low pressure. It dips down from the pole, allows arctic air to seep southwards.
ELOY: Which isn't to say the polar vortex wasn't involved in this bout of unseasonably cold weather. Masters says the typhoon that hit Alaska last week pushed one of those troughs of arctic air south across the Eastern U.S. Steven Nelson with the National Weather Service says these temperature shifts serve a purpose.
STEVEN NELSON: These cold intrusions, cold fronts are really restoring the balance in the temperature and moisture across the Earth's surface.
ELOY: A good chunk of the south is expected to get another wave of unseasonably cold weather starting Monday. Just don't call it the polar vortex. For NPR News, I'm Michell Eloy in Atlanta.
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