Climate forecasters often describe the Arctic Oscillation as the “wild card” of the winter forecast. So far in 2011, the Arctic Oscillation has been in its positive phase, playing the card that favors a milder winter in the eastern United States.
NOAA’s official Winter Outlook for 2011–2012 is unlikely to please many residents of either the still-soggy Missouri River Basin—which experienced historic flooding this past spring and summer—or the parched south-central United States, where severe to exceptional drought has been in place since spring.
The surface melt season on Greenland lasted up to 30 days longer than average in 2011, and it affected 31 percent of the ice sheet surface. Ice mass loss from Greenland in 2011 was about 430 gigatons—enough ice to raise global sea level by just over 1 millimeter.
Following a brief interlude of “neutral” sea surface temperature conditions this summer, La Niña has returned to the tropical Pacific Ocean. The cool phase of the El Niño-Southern Oscillation climate pattern is expected to persist through winter.