The polar vortex is the name given to the counterclockwise flow of air that occurs over the polar regions of a planet. On Earth, the vortex becomes less stable during winter, sending polar air away from the poles. 

Occasionally, changes in air pressure and wind help to diminish the “wall” of air containing the polar vortex, causing wobbles within the vortex. This unleashes cold air from the poles, allowing it to spread to other regions. This results in temperatures plummeting below -18°C (0°F) in major cities. In the United States, the weakened vortex can cause bitterly cold temperatures to reach as far south as Florida. The Antarctic’s polar vortex is stronger than its northern counterpart and not as susceptible to these wobbles.

Further Reading:

• The Rock Cycle
• Geography Notes