A deep freeze that gripped much of the United States and Canada in late January 2019 has been blamed on a polar vortex. The US National Weather Service warned that frostbite is possible within just 10 minutes of being outside in such extreme temperatures, and hundreds of schools, colleges and universities in the affected areas were closed. Around 21 people died in US due to severe frostbite. States within the midwest region of the United States had windchills just above -50°F (-45°C), which is colder than the frozen tundra and Antarctica. 