The extraordinarily cold, snowy weather that hit parts of the U.S. East Coast and Europe was the result of a collision of two periodic weather patterns in the Atlantic and Pacific Oceans, a study in the journal Geophysical Research Letters says.
Researchers at Columbia University say the anomalous winter was caused by two simultaneous weather events.
El Nino, the cyclic warming of the tropical Pacific, brought wet weather to the southeastern U.S. just as a strong pressure cycle called the North Atlantic Oscillation pushed frigid air from the arctic down the East Coast and across northwest Europe.
The end result, researchers say, was the snowiest winter on record for Washington, Baltimore and Philadelphia, bringing 6 feet of snow to the cities.
"Snowy winters will happen regardless of climate change," Columbia climate scientists Richard Seager says.
El Nino can be predicted months in advance by observing evolving conditions in the Pacific Ocean, but the North Atlantic Oscillation -- the difference in air pressure between the Icelandic and Azores regions -- is an atmospheric phenomenon, very chaotic and difficult to anticipate, study co-author Yochanan Kushnir says.