The piercing low temperatures come from an arctic air mass that drips down into North America.
“The polar vortex has split," said scientist Jennifer Francis with the Woods Hole Research Center in Massachusetts. "We now have two smaller circulations that trap cold air inside of them, but they have drifted outward. One of them over North America. So, not only are we having that run of the mill of transfer of cold air from Canada, which is kind of the typical thing, but we’re also seeing this reinforcement from this polar vortex in the stratosphere.”
Francis says a polar vortex split has been relatively rare but occurs more frequently in recent years. Research so far has pointed to climate change, a warm airmass that travels to the North Pole as a result of melting sea ice in Russia.
“When you have open ocean air instead of ice, a lot more heat from the ocean can be transferred up into the atmosphere which basically expands the layer of air because when air warms it expands. Think of a top spinning over the North Pole and here comes this bump that sends the top off wobbling away. If it wobbles enough it can cause the polar vortex to split.”
It’s likely it won’t happen again this year, but Francis says it’s not impossible.