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.
As much of the US experiences a dangerous and severe cold spell, does the UK have anything to worry about?
As the US battles sub-zero temperatures, ITV News Washington correspondent Robert Moore illustrates just how cold it is in Minnesota.
Leaders across America are urging residents to stay in their homes as "polar vortex" batters the east coast after snowstorm Hercules.