First of all,” he explains, “we are experiencing a La Niña pattern of sea surface temperatures in the Pacific Ocean. This pushes the jet stream and the cold arctic air northward.”
“On top of that, this year’s Arctic Oscillation has been stronger.”
The Arctic Oscillation is a see-sawing pressure difference between the Arctic and lower latitudes. When the pressure difference is high, a whirlpool of air forms around the North Pole. Last year, the whirlpool motion was weaker, allowing cold air to escape from the polar regions and head southward to the US.
“This year the whirlpool has been more forceful, corralling the cold air and keeping it nearer the pole. That has reinforced the La Niña impact.”
[“It ain’t over till the Siberian Huskies sing.”]
Source: Lennard Zinn