The polar vortex, or polar pig, as it has been dubbed by some media commentators, is:
- A large dense area of cold air formed in a polar winter
- Normally found rotating hurricane-like around the North or South Pole
- A low pressure area with winds that can exceed 100mph
- Around -80 degrees Celsius
- Strong enough to sustain its own low pressure, sealing in cold air like a fridge
- Tens of thousands of feet above the atmosphere
- Able to cause extremely cold conditions if its vortex is disturbed or deteriorates
- Rarely found in inhabited areas, but has moved south like an Arctic cyclone
- Possibly further south than normal due to a build up of warmer areas in Greenland or Alaska.
Chicago residents braved the outdoors today as a blast of Arctic air grips the mid-section of the US.
America is expecting its coldest temperatures in two decades, with meteorologists warning that temperatures were dangerously cold and life-threatening in some places.
Temperatures of -18 were recorded in Chicago - nicknamed "Chiberia" - St. Louis and Indianapolis, with the chill set to bear down on eastern and southern states as the day wears on.
Images by the National Oceanic and Atmospheric Administration show the polar vortex moving towards the east of the US today.
As the US battles sub-zero temperatures, ITV News Washington correspondent Robert Moore illustrates just how cold it is in Minnesota.Read the full story ›
Temperatures on the East Coast of the US have plummeted, with Chicago hitting lows of -15 this morning. The previous record for the Windy City was -14 in 1988.
NBC affiliate NBC Chicago tweeted a picture of Lake Michigan that appeared to show steam covering the Great Lake.
Chicago resident Jim Lakely posted a city-view picture that appeared to show the city's frozen river:
The anticipated 'polar vortex' is set to blast much of the country, with NBC reporting that "every state except Hawaii" is expected to face freezing temperatures today.
Large parts of the United States are bracing for freezing cold as a polar vortex is expected to drive temperatures to as low as -50C.
In Chicago, residents have been battling the elements as at least 20 centimetres of snow fell on Sunday.
The coldest place in the US after temperatures plummeted in the "polar vortex" is north Minnesota which currently stands at -34 degrees Celsius, according to a map published by NBC News.
Temperatures on the map are in Fahrenheit
As parts of the US are being hit by a polar vortex, which is expected to bring temperatures are low as -50C, residents of a small village in Russia deal with the freezing cold all year round.
The village of Oymyakon in the republic of Yakutia is the coldest place to live on Earth with the average temperature in the regions around -20C.
In 1933, a temperature of -67.8C was registered in the village - the lowest temperature ever recorded in the northern hemisphere.
It was also is the lowest temperature ever recorded for any permanently inhabited location on Earth.
Despite the harsh climate, approximately 5000 people live in the village, which has schools, a post office, bank, and even an airport runway (albeit open only in the summer).
Fans of the NFL's Green Bay Packers braved the lowest temperatures in two decades to watch their team play against the San Francisco 49ers on Sunday.
Packers fans were urged to wear multiple layers and hot drinks were handed out during the game.
Queen Mary 2 spent part of the weekend delayed in New York because of two feet of snow that fell in the United States.
She is now on her way say Cunard.
The liner is now racing home to Southampton for her tenth birthday celebrations on Friday where there be a big fireworks display.