Basking in this unusually balmy December? You can thank a weather phenomenon whose mere mention sends bone-chilling shivers down Americans' spines: the polar vortex.
But this time, instead of blanketing much of the nation in a brutal arctic blast, the polar vortex is keeping the deep freeze away. That's because the vortex — an arctic cyclone of extremely cold air high up in the atmosphere — is strong right now and fencing all that cold up north, meteorologists say.
"The jet stream has been to our north and we haven't seen it coming south," said James Mitchell, a National Weather Service meteorologist in Buffalo. "It's keeping all the cold air bottled up into Canada."