[7] El Niño Slowly Subsiding

The El Niño weather pattern that has been responsible for the Northwest's extra-mild winter and low precipitation is expected to last through the spring, but climate scientists say it's finally on its way out.

In a March 17 update, the Australian Bureau of Meteorology said "computer models suggest Pacific Ocean temperatures will cool steadily over the coming months, returning to neutral levels during the southern autumn. Such timing is typical of the decay stage of an El Niño event."

The Aussies said that subsurface ocean waters in the central Pacific had cooled since March 1 following some renewed warming in February, after trade winds weakened over the western and central Pacific during late January and early February.

But they also said eastern Pacific subsurface waters had warmed slightly, though surface temperatures were headed lower near the South American coast.

Data from a satellite that measures wave heights indicated that a large wave of warm water (called a Kelvin wave) was moving eastward from the area of weakening trade winds. It's just one of several that were spawned by the latest El Niño.

The Aussies' Mar. 31 update said, "The most noticeable feature of the past fortnight has been the decrease in Pacific Ocean heat content, with values east of the dateline dropping to their lowest values since April 2009, indicating the deeper ocean is also slowly cooling. Likewise, sea surface height in the central and eastern Pacific is also decreasing."

In a recent press release from the Jet Propulsion Lab, oceanographer Bill Patzert said he would not be surprised if this latest and largest Kelvin wave is the "last hurrah" for this long-lasting El Niño.

"Since June 2009, this El Niño has waxed and waned, impacting many global weather events," said Patzert. "I, and many other scientists, expect the current El Niño to leave the stage sometime soon. What comes next is not yet clear, but a return to El Niño's dry sibling, La Niña, is certainly a possibility, though by no means a certainty. We'll be monitoring conditions closely over the coming weeks and months."

The April 5 NOAA El Niño update said most computer models predicted a return to neutral conditions by July, but several others pointed to the "potential" of continued El Niño conditions or a shift into La Niña conditions by next fall.

The current January-through-July water supply forecast from NOAA's Northwest River Forecast Center calls for only 65 percent of average for the Columbia River at The Dalles, and that could go lower. March precip levels for the Columbia Basin above both Grand Coulee and The Dalles have been 81 percent of average. -B. R.

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