PACIFIC OCEAN — A December “El Niño/Southern Oscillation” update by the National Weather Service’s Climate Prediction Center (CPC) that during November 2010, the ongoing La Niña, which began early this summer, was reflected by below-average sea surface temperatures across the equatorial Pacific Ocean. 

The subsurface oceanic heat content (average temperatures in the upper 1,000 feet of the ocean) also remained well below-average in association with a shallower-than-average thermocline across the central and eastern equatorial Pacific. Enhanced low-level easterly trade winds and anomalous upper-level westerly winds continued over the equatorial Pacific. 

“Collectively, these oceanic and atmospheric anomalies reflect a moderate-to-strong La Niña,” the update says. Impacts from such climatic conditions in the U.S. include an enhanced chance of above-average precipitation in the Pacific Northwest.

The CPC’s three-month “outlook” issued Dec. 16 forecasts a greater than 40 percent chance of above normal precipitation throughout Washington and Montana, across northern Oregon in central and northern Idaho. That forecast for January through March sees an equal chance of below-, near-, or above-normal precipitation in southern Idaho and Oregon.

La Niña is expected to peak during November through January and to continue into the spring of 2011, according to the CPC update. 

“Thereafter, the fate of La Niña is more uncertain,” the update says. Most forecasts indicate a return to ENSO-neutral conditions during the spring and early summer, but a few “suggest that La Niña could persist into the summer. Historically, there are more multi-year La Niña episodes than El Niño episodes, but other than support from a few model runs, there is no consensus for a multi-year La Niña at this time.”

A late spring drenching and the strong start to the new water year have all but eliminated drought conditions in the Northwest except for a small patch in south-central Oregon, according to the federal U.S. Drought Monitor’s December update.

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