BRACE YOURSELVES The polar vortex could be back as soon as next week after a three-year hiatus, ready to bring record-low temperatures to much of North America, according to forecasters. The coldest weather is expected to hit the midwest and northeast starting Tuesday. A polar vortex is a cold air mass that generally hovers over the poles - as its name suggests - but can shoot over the U.S. thanks to a jet stream. The big chill comes after the warmest ever October-through-November period.
