Polar Vortex Formation

Polar vortex formation is the seasonal strengthening, as autumn darkness sets in over a pole, of a large, persistent low-pressure area of cold cyclonic circulation that sits in the middle and upper troposphere and stratosphere through winter, driven by the temperature contrast between the pole and the mid-latitudes. A strong, stable vortex keeps the coldest air locked over the pole, while a weakened or disrupted vortex, a sudden stratospheric warming being the extreme case, allows lobes of that cold air to spill southward into the mid-latitudes, the mechanism behind many severe winter cold outbreaks. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/