https://phys.org/news/2019-01-science-polar-vortex-outbreaks.html

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.