The Arctic Oscillation describes simultaneous, geographically “choreographed” shifts in multiple features of the polar vortex: air pressure, temperature, and the location and strength of the jet stream. They all follow the hemisphere-wide oscillation of atmospheric mass back and forth between the Arctic and the middle latitudes, sort of like water sloshing in a bowl.

A few days of unusually cold weather in the U.S. and Canada aren't a sign that a century-or-more trend of rising global surface temperatures has reversed itself. In fact, the cold wasn't even all that widespread for the Northern Hemisphere.

globes showing pressure patterns during positive and negative phases of the Arctic Oscillation

Large-scale shifting of the weight of the atmosphere between mid- and high latitudes creates climate patterns known as the Arctic and North Atlantic Oscillations. These patterns have a big influence on winter weather in the Eastern U.S.

The Arctic Oscillation (AO) refers to an atmospheric circulation pattern over the mid-to-high latitudes of the Northern Hemisphere. The most obvious reflection of the phase of this oscillation is the north-to-south location of the storm-steering, mid-latitude jet stream.

Was El Niño to blame for the above-average temperatures during November and December 2015?  As always, the answer is not that simple.