It's back!

A chunk of the polar vortex is forecast to slide over the central and eastern United States over the next few days, marking its first unwelcome visit of the season. In many locations, temperatures will be more like mid-January than mid-November.

"It’s time to start talking about the polar vortex," said weather.us meteorologist Ryan Maue. “If your furnace is on the fritz, then perhaps it's a good time to get that fixed.”

Through much of the rest of this week, high temperatures in parts of the northern Rockies and northern Plains will struggle to rise above 32 degrees each day, the Weather Channel said. For example, Bismarck, North Dakota, may only briefly rise above freezing this weekend.

The cold will sweep into the Northeast by the weekend, where daytime highs may struggle to get out of the 30s and 40s Saturday and Sunday.

Snow is also coming with the cold in some areas, including across the central Plains on Wednesday night into Thursday, where 2-6 inches of snow is forecast.

Snow is also likely Friday and Saturday near the Great Lakes, including potentially heavy lake-effect snow in the usual snowbelt regions of Michigan, Ohio, Pennsylvania and New York, according to AccuWeather.

Lake-effect snow, which can last for only a few minutes to several days, falls from narrow bands of clouds that form when cold, dry arctic air passes over a large, relatively mild lake. These snows can occur only in the fall or early winter, before the lakes freeze over.

"The frigid air passing over the still-warm Great Lakes will increase chances for lake-effect snow," said AccuWeather meteorologist Steve Travis. It could be the first major lake-effect snow event for many, he added.

In heavier snow bands, there could be enough snow piling up to require plowing and shoveling.

The cold forecast has sent natural gas prices soaring, CNBC reported.

If the cold persists this fall and winter, natural gas prices could rise above $5 or $6 per million British thermal units – a measurement of energy – for weeks at a time, Jen Snyder of RS Energy told CNBC. Traders have not seen those price levels since the polar vortex that plunged the United States into extreme cold during winter 2014, she said.

What is the polar vortex?

The polar vortex is a large area of cold air high up in the atmosphere that normally spins over the North Pole (as its name suggests), but thanks to a meandering jet stream, some of the vortex can slosh down into North America, helping to funnel unspeakably cold air down here where we live.

The vortex has likely "existed in some form for the past 4.5 billion years," according to senior scientist Jeff Kiehl of the National Center for Atmospheric Research in Boulder, Colorado. Although it's been understood by scientists for several decades, it only entered the popular lexicon as a synonym for miserably cold winter weather a few years ago.

The vortex is strongest during the winter and usually weakens or even disappears in the summer. Its position determines what part of the USA the Arctic air will invade.

If you're looking for a return to milder weather in the East, you may be in luck. After this Arctic blast, temperatures may rebound to average or even above-average levels later in November, according to Judah Cohen, a meteorologist with Atmospheric and Environmental Research (AER). This is because the polar vortex should return to its rightful place way up north, awaiting its next, yet-to-be-determined visit.