The meteorological term "polar vortex" has a dramatic and ominous sound—the title of a disaster movie, maybe. But it is a just pattern of winds that is with us all the time and played a big role in recent deep cold snaps. They occur when the southern edge of this weather system pushes farther south than usual. Martha Foley and Curt Stager take a little of the hype out of this winter's weather buzz-word.