A blast of brutally cold air – thanks to the polar vortex – is roaring across the central and eastern USA this week, sending temperatures to levels not seen in 20 years.

The polar vortex is a strong area of low pressure that usually wanders around the Arctic throughout the winter. This week, the core of the vortex has actually slipped all the way down over the USA.

Frigid air that snapped decades-old records made venturing outside dangerous for many days, the cold spreading to southern and eastern parts of the U.S. has been keeping many schools and businesses shuttered.

Polar Pics

Check out some of the more dramatic snaps from some of the coldest days in US history, with temperatures dropping well below 0 degrees!