It is colder than Antarctica in many parts of the USA. This is because of a polar vortex - freezing air and wind from the Arctic. This rarely happens. There is a state of emergency in many towns. Schools and businesses have closed. People were told not to travel. They were told not to go outside or breathe the icy air.
The temperature in a part of Minnesota fell to -60º Celsius. The Chicago River and Niagara Falls turned to ice. The cold killed eight people. Officials told people to go outside only if necessary. Freezing air can be dangerous for the skin. It can cause breathing problems. Shoveling snow can also be dangerous.