The latest public enemy No. 1 comes complete with an ominous, super-villain name and a tendency to waver drunkenly around the Northern Hemisphere, leaking great, vast gasps of frigid Arctic air into normally more temperate latitudes.
But what is the polar vortex, and why has it been making so much trouble over the last few winters?
First off, there's the scary name. It comes from the fact that when viewed from above the North Pole, the polar vortex forms a river of air that spins in a rough circle, around the hemisphere from west to east. It's always been there, but most of the time it minds its own business and serves as a wall of wind to hold wintry Arctic air where it belongs -- in the Arctic. But this week it's not doing that.
"That wind can look like an ellipse or it can be wavier," explained James Overland, a senior scientist at the NOAA/Pacific Marine Environmental Laboratory in Seattle. "That wavy pattern is what we are seeing today."
The waviness is usually bad news for the Eastern United States because that region is already on the edge of a back up and turn in the vortex's river of air, caused by the obstruction of the Greenland's mountains, Overland said.