The researchers identified several
key circulation
patterns that affected the winter temperatures from 1979 to 2013, particularly the Arctic Oscillation (a climate
pattern that circulates around the Arctic Ocean and
tends to confine colder air to the polar latitudes) and a second
pattern they call Warm Arctic and Cold Eurasia (WACE), which they found correlates to sea ice loss as well as to particularly strong winters.
El Niño is a
key factor in making hurricane seasonal forecasts because the changes in atmospheric
patterns over the tropical Pacific that it ushers in have a domino effect on
patterns over the Atlantic,
tending to suppress hurricane formation.