It irks me when the media latches on to a weather term that sounds cool, or maybe even threatening, and goes crazy with it - until the general public has no idea what it is, or thinks it's something it's not.
I've heard Polar Vortex thrown around on the network news today, and on our local newscast. It sounds cold (Polar) and twisty (Vortex). Is it some kind of new global storm!!!???
Back in the day, they probably just called it cold air.
The Polar Vortex is simply the general circulation around the Arctic air in the Polar regions. It's surrounded by the global-scale river of air (jet stream) flowing over the northern latitudes. It's a counter-clockwise circulation in the upper-levels (low pressure), usually keeping the Arctic air masses locked in place near the North Pole or Siberia. It's a persistent, large-scale cyclone, located year-round near the poles.
The American Meteorological Society's definition: Polar Vortex,
(Also called polar cyclone, polar low, circumpolar whirl.) The planetary-scale cyclonic circulation, centered generally in the polar regions, extending from the middle troposphere to the stratosphere.
The vortex is strongest in winter when the pole-to-equator temperature gradient is strongest. In the Northern Hemisphere, the vortex has two centers in the mean, one near Baffin Island and the other over northeast Siberia."
CNN recently wrote up a good FAQ about the Polar Vortex.
It is not a storm. It is not on a local scale. You can't look out your window and see it whizzing by.
The Polar Vortex can get displaced or disrupted, and when the jet stream dives down, it shifts the Arctic air south. This is why it's so cold right now. When the jet stream digs a trough, the cold air dives south. A ridge is the opposite, and our air warms up.
You can see the circulation well south of it's "normal" homeland near the Great Lakes in the image below (The US is at the very bottom). The blue shading is the jet stream, or the strong winds at high levels in the atmosphere.