Temperatures in the eastern tropical Pacific Ocean swing back and forth like an irregular pendulum. The cool phase—which the Pacific has been in for the past two winters—is called La Niña. According to NOAA’s April 2012 ENSO Diagnostics Discussion, La Niña is fading and will likely be over by the end of April.
When NOAA’s National Climatic Data Center crunched the numbers for December, January and February—”meteorological” winter for 2011-2012—it stacked up as the fourth warmest of the past 117 winters. Virtually all of the West received less than its average precipitation.
Modeling predicts that increasing greenhouse gas emissions will significantly increase thermal stress on Pacific Northwest salmon in coming decades, making the hard job of restoring endangered wild salmon even harder.
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.