By Seth Borenstein
It might seem counterintuitive, but the dreaded polar vortex is bringing its icy grip to parts of the U.S. thanks to a sudden blast of warm air in the Arctic.
Get used to it. The polar vortex has been wandering more often in recent years.
It all started with misplaced Moroccan heat. Last month, the normally super chilly air temperatures 20 miles above the North Pole rapidly rose by about 125 degrees (70 degrees Celsius), thanks to air flowing in from the south. It's called "sudden stratospheric warming."
That warmth split the polar vortex, leaving the pieces to wander, said Judah Cohen, a winter storm expert for Atmospheric Environmental Research, a commercial firm outside Boston.
"Where the polar vortex goes, so goes the cold air," Cohen said.
By Wednesday morning, one of those pieces will be over the Lower 48 states for the first time in years. The forecast calls for a low of minus 21 degrees (minus 29 Celsius) in Chicago and wind chills flirting with minus 65 degrees (minus 54 Celsius) in parts of Minnesota, according to the National Weather Service.
The unusual cold could stick around another eight weeks, Cohen said.
"The impacts from this split, we have a ways to go. It's not the end of the movie yet," Cohen said. "I think at a minimum, we're looking at mid-February, possibly through mid-March."
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