What you need to know about the polar vortex

In the Midwest and Northeast of the US, residents should prepare for temperatures 20 to 30 degrees below the average.

Andrew Kelly/Reuters
People walk through downtown Manhattan in New York on February 14, 2016, when an earlier polar vortex pushed temperatures well below freezing.

Many Americans are bundling up this week, as frigid temperatures mark the return of the polar vortex.

Scientists say that although many of us will feel the vortex’s chilly effects intensely this week, the phenomenon is actually a constant in our lives – the low pressure system swirls above the North Pole year-round. Come winter, it sends freezing air southward to us.

"The polar vortex doesn't come and go. It does weaken and strengthen, and that's how it fuels the weather around the world," according to NBC News meteorologist Sherri Pugh.

And contrary to popular belief, although the polar vortex does send wintry temperatures along, it does not impact the weather system. This means that unfortunately, you can’t blame the vortex if the predicted snow later this week makes driving difficult.

"It [the polar vortex] is actually in the stratosphere. Our weather happens in the lower level of the atmosphere, and this occurs just right above that lower level," said Ms. Pugh.

Although the term “polar vortex” entered popular parlance just a few years ago, the concept has been around since the mid-19th century. Recently, the same phenomenon that made the winter of 2014 a winter to remember also occurred in 1977, 1982, 1985, and 1995.

Nevertheless, this year’s polar vortex seems to be a bit early, and scientists have noted that climate change could be changing the vortex somewhat as time goes by.

"Global warming did not create polar vortexes, though the changing climate might be changing the nature of them," Weather Channel meteorologist Stu Ostro wrote in early 2014. "Nor did humans create the term this week ... it's been an accepted scientific one for at least 75 years."

Some areas of the country will have it worse than others this week, with the mercury dropping in states like Michigan and Montana to temperatures as low as 30 to 40 degrees below zero.

In most places, however, the vortex will bring temperatures that are merely 20 to 30 degrees lower than usual.

In the Northeast, daily temperatures are expected to be in the teens, while in the upper Midwest and northern Plains states, temperatures will likely fall into the single digits. Of course, those temperatures don’t consider windchill, so residents can expect to feel even chillier than the thermometer might indicate.

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