The Midwest has been hit by extreme freezing conditions this week. Parts of the Midwest will experience the coldest temperatures in over 20 years. A polar vortex which is causing extreme Arctic blasts could bring temperatures as low as -53°C.
The polar vortex is a circulation of winds in our stratosphere, about 50km above the earth. It can cause extremely cold and wintery weather when the jet stream weakens, drawing cold Arctic air with it. For more information about the polar vortex please follow this article by the Met Office - https://www.metoffice.gov.uk/learning/atmosphere/polar-vortex.
Some parts of the Midwest have been forecast to be colder than parts of Antarctica. The National Weather Service has issued wind chill warnings and a high risk of frostbite within ten minutes of being outside. Bitterly cold temperatures are forecast to reach parts of the Northeast in the USA later this week. https://weather.com/forecast/national/news/2019-01-28-polar-vortex-midwest-arctic-air-coldest-two-decades.