With the Midwest and Great Lakes regions in the midst of a life-threatening polar vortex, it's helpful to understand how extreme cold environments affect the human body.

This week, some US cities are experiencing record-breaking, low temperatures that are colder than most parts of Antarctica. And unfortunately, these weather systems might be getting more common.

This kind of severe winter weather can cause some serious health effects. Here are eight ways the freezing temperatures can affect your body.</s>[For the latest on the weather in the Midwest, read our Friday updates here.]

CHICAGO — Midwesterners trudged ahead Thursday into a familiar, grim reality: temperatures well below zero, schools and businesses closed, stern warnings to wear extra layers or, better yet, just stay indoors.

The polar vortex that arrived earlier this week has for days disrupted life across an entire region. Deaths and injuries were reported. Decades-old records fell. And, for one more day, even stepping outside remained a painful, risky experience.

But the forecast finally suggested relief ahead. By Thursday night, temperatures across much of the Midwest were expected to poke above zero. By the end of the weekend, meteorologists predicted as much as a 70- or 80-degree swing, with balmy-for-February readings in the 40s or 50s and rain instead of snow.

Still, risks remained. A band of snow complicated travel on Thursday, and in the Northeast, officials warned of their own cold wave, with heavy snow in some places and subzero wind chills in others.</s>Do you know what the polar vortex is and how it can affect the weather?

A polar vortex is a low-pressure area—a wide expanse of swirling cold air—that is parked in polar regions. During winter, the polar vortex at the North Pole expands, sending cold air southward...and is often associated with outbreaks of cold temperatures...Sometimes this low-pressure system, full of cold Arctic air, strays a little bit too far from home. Part of it can break off and migrate southward, bringing all of that cold air with it...The breaking off of part of the vortex is what defines a polar vortex event...[ Scijinks.Gov ]

A polar vortex is simply a semi-permanent, massive low-pressure system that hovers over the poles of our planet.

The National Weather Service says the polar vortex ALWAYS exists near the poles:
• The polar vortex weakens in summer and strengthens in winter.
• The term "vortex" refers to the counter-clockwise flow of air that helps keep the colder air near the Poles.
• During winter in the northern hemisphere, the polar vortex will expand, sending cold air southward with the jet stream (see graphic above). This occurs fairly regularly during wintertime and is often associated with large outbreaks of Arctic air in the United States.

According to the National Weather Service , the polar vortex is NOT:
• Polar vortexes are not something new. The term “polar vortex” has only recently been popularized, bringing attention to a weather feature that has always been present.
• It's not a feature that exists at the Earth’s surface. Weather forecasters examine the polar vortex by looking at conditions tens of thousands of feet up in the atmosphere; however, when we feel extremely cold air from the Arctic regions at Earth’s surface, it is sometimes associated with the polar vortex.
• Polar vortexes are not confined to the United States. Portions of Europe and Asia also experience cold surges connected to the polar vortex. By itself, the only danger to humans is the magnitude of how cold temperatures will get when the polar vortex expands, sending Arctic air southward into areas that are not typically that cold.
• Keep your cell phone charged and make sure you know where your backup power supply is.
• Make sure all your flashlights have fresh batteries.
• Fill your gas tank. You can use your car to keep warm and recharge devices.
• Have some food available that you don’t need to cook.
• Download the Eagle App You’ll receive local alerts, weather reports and more with push notifications.</s>The polar vortex in the US continued inflicting severe conditions across the country on Thursday, with temperatures reaching minus 40F - and a town in Michigan called Hell quite literally freezing over.

Chicago was on track to break the city’s record of -32C (-26F), set more than 30 years ago as the cold snap intensifies.

Some nearby isolated areas could see temperatures as low as -40C (-40F), that would break the Illinois record of minus 38C (-36.4F) set in 1999.

Milwaukee had similar conditions. Minneapolis recorded -32C (-26F) while Sioux Falls, South Dakota, saw -31C (-24F).

Wind chills reportedly made it feel like -45C (-49F) or worse.

The blast of polar air that enveloped much of the Midwest on Wednesday closed schools and businesses and strained infrastructure with some of the lowest temperatures in a generation.

The deep freeze snapped rail lines, cancelled hundreds of flights and strained utilities.

Trains and buses in Chicago operated with few passengers as the hardiest commuters ventured out only after covering nearly every square inch of flesh against the extreme chill, which froze ice crystals on eyelashes and eyebrows in minutes.

Crews in Detroit will need days to repair water mains that burst on 30 January, and other pipes can still burst in persistent subzero temperatures.

Temperatures are expected to improve later this week and more people are expected to return to work in the nation’s third largest city.

Meanwhile, cities like Chicago reportedly experienced "frost quakes," a phenomenon caused by freezing and expanding water under the ground and causes earthquake-like effects.

See The Independent's live coverage of the polar vortex across the United States on Thursday as it happened below:

Please allow a moment for the liveblog to load</s>Polar vortex: What are they and why are they happening?

Polar vortex: What are they and why are they happening?

Temperatures of -70C (-94F), dire warnings about going outside, schools and businesses closed and travel plans left in limbo.

In a polar vortex such as that gripping the US, even breathing can be dangerous. But what is this devastating phenomenon that seems increasingly common and whose icy grip makes daily life so difficult?

"A large area of low pressure and cold air surrounding the north and south poles," is how the National Oceanic and Atmospheric Administration defines it.

Present all year round, it is known as a "vortex" because the air flows anti-clockwise, keeping the colder air close to the poles.

It sits about 30 miles (48km) above Earth's surface, around 20 miles (32km) above the jet stream, a meandering river of strong westerly winds around the Northern Hemisphere.

When uneven warm air disrupts it from below, causing the jet stream to weaken and buckle, eddies of cold air, such as the one currently sitting over the US, are pushed down, sending warmer air into Alaska and pushing cold winds down into the US Midwest and East Coast.

How cold can they get?

The current polar vortex sitting over the US is set to break records. In Minnesota, temperatures could drop as low as -70C (-94F) with wind chills, prompting authorities to warn about the dangers of going outside or even just breathing.

Chicago is forecast to be as cold as parts of Antarctica.

Why is the US vulnerable to them?

The country's location and size makes them common, but they affect other countries, too. The UK endured a polar vortex last winter but temperatures were much less extreme than is common in parts of the US. They can occur anywhere in the Northern Hemisphere.

Are they new?

They may feel like a creature of the 21st century but they have been around "forever", US National Weather Service meteorologist Mark Chenard said. It is thought that the term first appeared in 1853.

Are they caused by climate change?

Scientists are divided on this. Mr Chenard said the phenomenon was not related to global warming, but others disagree. Jennifer Francis, senior scientist at the Woods Hole Research Centre, said there was evidence that changes in the Arctic stratosphere were causing polar vortexes to become more regular.

Scientists have said that higher temperatures in the Arctic have led to historically low levels of ice there and that this, in turn, has caused changes in the jet stream, forcing the polar vortex to buckle.

Ms Francis cautioned against seeing the latest example of the phenomenon as evidence "global warming is a hoax" - which appeared to be Donald Trump's assessment when he tweeted about the vortex.</s>The polar vortex in the US is expected to see records tumble as temperatures reach minus 40F - and a town in Michigan called Hell freezes over.

Chicago is expected to break the city’s record of minus 26F (minus 32C), set more than 30 years ago as the cold snap intensifies.

Some nearby isolated areas could see temperatures as low as minus 40F (minus 40C), that would break the Illinois record of minus 38C set in 1999.

Please allow a moment for the liveblog to load

Milwaukee had similar conditions. Minneapolis recorded minus 26F (minus 32C) while Sioux Falls, South Dakota, saw minus 24F (minus 31C).

Wind chills reportedly made it feel like minus 49F (minus 45C) or worse.

Trains and buses in Chicago operated with few passengers as the hardiest commuters ventured out only after covering nearly every square inch of flesh against the extreme chill, which froze ice crystals on eyelashes and eyebrows in minutes.

The blast of polar air that enveloped much of the Midwest on Wednesday closed schools and businesses and strained infrastructure with some of the lowest temperatures in a generation.

The deep freeze snapped rail lines, cancelled hundreds of flights and strained utilities.

Crews in Detroit will need days to repair water mains that burst on 30 January, and other pipes can still burst in persistent subzero temperatures.

Temperatures are expected to improve later this week and more people are expected to return to work in the nation’s third largest city.</s>A pedestrian stops to take a photo by Chicago River as bitter cold phenomenon called the polar vortex has descended on much of the central and eastern United States - REUTERS

Tens of millions of people in the United States are bracing for a potentially life-threatening deep arctic chill forecast to hit swaths of the country on Wednesday.

Companies have told their workers to stay home, schools are closed and hundreds of flights have been canceled.

The US Postal Service - known for its commitment to bringing the mail whatever the weather - has even reportedly suspended deliveries in Iowa due to the severe cold.

Temperatures in almost a dozen states stretching more than 1,200 miles (1,930 kilometers) from the Dakotas to Ohio were forecast to be the coldest in a generation, if not on record.

"One of the coldest arctic air mass intrusions in recent memory is surging south into the Upper Midwest before spreading across much of the eastern two-thirds of the country," the National Weather Service said.

"Expect frigid temperatures, bitterly cold and life-threatening wind chills, likely leading to widespread record lows and low maximum temperatures from the Upper Midwest to the Great Lakes and Ohio Valley."

The cause is a swirl of arctic air that broke away from the polar vortex that usually encircles the North Pole.

The National Weather Service forecast temperatures between -10 to -40 degrees Fahrenheit (-23 to -40 Celsius) by Wednesday across the Midwest, with wind chills making it seem as cold as -65 degrees Fahrenheit in one area of Minnesota.

Chicago, America's third largest city, was expected to be colder than parts of Antarctica.

Authorities in Illinois, Michigan and Wisconsin put emergency measures in place to handle the frigid weather.

"We need everyone to do your part and make sure you and your families are prepared," said Illinois Governor JB Pritzker.

Americans were asked to stay home if possible Wednesday, when temperatures are expected to be at their coldest.

Scores of schools, businesses and government agencies announced closures in multiple states.

"People exposed to extreme cold are susceptible to frostbite in a matter of minutes," warned the NWS.

Lawrence Gottlieb of the University of Chicago Medical Center said the threat was significant "when temps fall below zero, especially when there is a strong wind."

Some 160 warming centers were opened in Chicago, where temperatures could potentially equal or exceed the all-time record of -27 degrees Fahrenheit. With the wind chill, it would feel like -40 or -50, officials said.

"They are life-threatening conditions and temperatures," Chicago Mayor Rahm Emanuel told a news conference. In Minneapolis, officials allowed residents to stay on public buses and trains for warmth. The @NWSDesMoines regarding the upcoming cold in the Upper Midwst and Great Lakes: "This is the coldest air many of us will have ever experienced." https://t.co/OykrGHmgoU — Capital Weather Gang (@capitalweather) January 27, 2019 In the northeastern and southern United States, snow was falling. A cold emergency was declared in the US capital Washington, with additional services put on for the homeless. In Atlanta, some 300 flights were canceled Tuesday as the city prepares for the Super Bowl and more than 400 were canceled in Chicago, a major regional hub for US airlines. In Canada, the icy temperatures - stretching from Manitoba in the western Prairies region to the Atlantic seaboard - prompted a rare "hazardous" cold warning from the government. Environment Canada reported record-breaking snowfall at the Ottawa airport, where some 50 flights were canceled, with an accumulation of nearly a meter (more than three feet). An additional 200 flights were canceled at Toronto's airport. Scientists say climate change is causing more extreme weather, and one theory for polar vortex chills is that arctic air currents usually trapped around the North Pole are weakened and dislodged by a warming climate. WC MN we’re dealing w/some limited visibility in the open areas. Remember to turn those headlights & taillights ON and #MoveOver for those on the shoulder. This area was I-94 about 10 miles east of Moorhead. Road info https://t.co/UtVIO3kuBrpic.twitter.com/yZG4NRC5Th — Sgt. Jesse Grabow (@MSPPIO_NW) January 29, 2019 President Donald Trump used the occasion to again voice skepticism about climate change, tweeting: "What the hell is going on with Global Waming? (sic) Please come back fast, we need you!" But the National Oceanic and Atmospheric Administration, which operates NWS, tweeted, "Winter storms don't prove that global warming isn't happening," with a link to a 2015 explanatory article.</s>A blast of Arctic-chilled air from the polar vortex has reached the US as temperatures drop to as low as -46C (-50F) in Chicago. Cities in the midwest opened warming shelters as temperatures plummeted well below zero. 'This storm poses a serious threat to the wellbeing of people around the state, and we will use every tool at our disposal to keep our residents safe,' said the Illinois governor, JB Pritzker, in a statement on Tuesday.

The freezing weather was caused by the polar vortex, a mass of freezing air that normally spins around the north pole. But this time it made its way south in the US.</s>At least 10 people have died in connection with snow and dangerously cold temperatures across the midwestern section of the United States, authorities said Thursday.

The temperature in International Falls, Minnesota, dipped to minus 45F (minus 43C) early Thursday just south of Canada. The city, dubbed the "Icebox of the Nation," saw temperatures drop another 5 degrees F early on Thursday.</s>If you’ve been watching the news this week, you’ve probably heard the term polar vortex referenced regarding some exceptionally cold temperatures expected for areas of North America.

So what is the polar vortex? The polar vortex is a semi-permanent area of low pressure under which is contained exceptionally cold Arctic air. “Polar” for its typical position near the North Pole and “vortex” for the counter-clockwise motion that all low-pressure systems induce in the atmosphere in the Northern Hemisphere. The term dates back to 1853 in its use in the field of meteorology.

For much of the year, the polar vortex is contained within the Arctic Circle. Occasionally (and most frequently during our winter season) the polar vortex becomes unstable and breaks into waves of cold Arctic-source air that can dip down south and move across more southern areas of North America. One of these waves of cold Arctic air is currently moving across and impacting areas of Canada and the United States. Through the start of this week it broke down and south through Saskatchewan and Manitoba into Ontario and the mid-western U.S. Through the end of this week and weekend it will traverse Quebec, Labrador, and eventually moderate over the ocean waters of the North Atlantic next week.

While this does happen during our winter season, this particular episode is more extreme than typical. It has resulted in dangerous wind chills making it feel close to -50 for areas of Saskatchewan and Manitoba on Wednesday and a large swath of extreme cold warnings for central and Eastern Canada. Those types of wind chills can create frostbite in five minutes or less to exposed skin. It also set new low temperature records for parts of Central Canada and the mid-western U.S. The coldest temperature in Canada on Wednesday was at Key Lake, Sask., at -47.2 C, beating out even much more northern locations such as Shepard Bay, NU, (-44.7 C) and Hanbury River, NT, (-43.3 C).

The Maritimes will be impacted by this breakdown in the polar vortex later this week and into the weekend. It will be more of a brush-past than a direct hit for us, though it will get plenty cold as the Arctic-sourced air moves in. Northern New Brunswick will catch the brunt of it with temperatures well down into the minus teens and 20s Thursday night. The wind chill will make it feel closer to -30 C on Friday morning. Wind chills in other areas of the Maritimes will make it feel into the minus teens and 20s at times Thursday through Sunday.

The cold air will began to moderate substantially on Monday and Tuesday.
Several cities in the Midwestern United States and Eastern Canada reach record low temperatures for the third consecutive day as a polar vortex continues to affect the region.