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'La Nina' Now Reigns PNW Weather; Colder Ocean Should Be Boost To Basin Salmon Survival
Posted on Friday, August 13, 2010 (PST)

An already chilled northeast Pacific Ocean and rapidly cooling equatorial sea surface temperatures likely bode well for Columbia River basin salmonids that start and end their lives in freshwater but spend most of their lives at sea.


The late winter and early spring saw a fading of "El Nino" conditions -- elevated sea surface temperatures in the central and eastern equatorial Pacific -- that had prevailed over the fall and winter.


El Nino conditions can affect climatic conditions worldwide as well as ocean conditions outside the equatorial zone. El Nino's presence tilts the odds toward warmer and drier conditions in the Pacific Northwest during the fall and winter.


The reverse is true when La Nina conditions reign. And they do now reign, according to meteorologists.


"During July 2010 La Nina conditions developed, as negative sea surface temperature anomalies strengthened across the central and eastern equatorial Pacific Ocean," according to an ENSO (El Nino/Southern Oscillation) alert issued Aug. 5 by the National Weather Service's Climate Predictions Center.


All indicators in the Pacific Ocean show that we are now in the early stages of a La Niña event. Computer models predict the central Pacific will continue to cool in coming months, indicating some further strengthening of the event is likely, according to the Aug. 4 ENSO Wrapup produced by the Australian government's Bureau of Meteorology.


"Signs of an emerging La Niña event have been apparent in the equatorial Pacific for several months," the Australian agency says. "Pacific Ocean temperatures have cooled steadily throughout the year, the Southern Oscillation Index (SOI) has increased in value and is currently around +21, trade winds continue to be stronger than average and cloudiness has remained suppressed over the central Pacific. All of these key indicators have now reached or exceed La Niña levels."


"Given the strong cooling observed over the last several months and the apparent ocean-atmosphere coupling (positive feedback), the dynamical model outcome of a moderate-to-strong episode is favored at this time," the CPC alert says. "Therefore, La Niña conditions are expected to strengthen and last through Northern Hemisphere Winter 2010-11."


"All indications are that surface and subsurface water is cooling" to establish La Nina conditions, said Kyle Dittmer, the Columbia River Inter-Tribal Fish Commission meteorologist. "All signs of El Nino have gone away."


The signs of El Nino began eroding in March and La Nina signs have been growing since May to the point this month of an official CPC declaration.


"La Nina conditions are likely to continue through early 2011," the CPC says.


Coincidentally, or maybe not, water temperatures off the coasts of Washington and Oregon turned very cold this late spring and summer. And the upwelling of nutrients that feed plankton that feed young fish began, though belatedly, in early July in strength. The upwelling can begin as early as April.


"It's looking pretty vigorous," Dittmer said of the upwelling indices.


NOAA Fisheries oceanographer Bill Peterson said that during a mid-July data collection cruise out of Newport, Ore., surface water near-shore (1 mile from shore) was the coldest ever measured over 15-year course of an ongoing ocean indicators study and the deep water at the study's five mile station was the fourth coldest in 15 years. Both are very positive indicators for fish, he said.


The researchers sample the coastal waters off Newport at biweekly intervals during the ocean upwelling season in spring, summer, and fall. The Northwest Fisheries Science Center crew samples various physical ocean conditions, such as temperature and salinity, as well as biological conditions such as the productivity of the food web and availability of food for salmon.


"The ocean's very cold. Typically that's been very good for the food web," said Nathan Mantua, an atmospheric research scientist at the University of Washington and co-director for the school's Center for Science in the Earth System.


"Survival for chinook and coho tends to be very high when conditions are like this," Mantua said.


He said that the cooled coastal ocean is probably not La Nina linked but more likely the result of winds and other atmospheric phenomenon. It does give the ocean that welcomes young Columbia River salmon outmigrants a head start. A cool northeast Pacific is, eventually, a consistent end product of El Nino. So an early start means those favorable conditions for a longer period.


The fact that the northeast ocean is already chilled and the negative (cool) sea surface anomalies at the equator show a continued strengthening "give us some confidence that that these conditions will persist into next summer," Mantua said.


The CPC says that the earliest that the Northwest can expect to experience impacts from the newly developed La Nina is this fall. The center's October-December long-range forecast is for a greater than 33 percent chance of above normal precipitation throughout the region, with the chances of the same exceeding 40 percent in north and central Idaho, western and northern Oregon, and all of Washington state. The temperature forecast for that period is for equal chances of below, near, and above normal weather in the region.


A wet winter would mean that an ample snowpack would build in the mountains that ring the Northwest and its Columbia River basin. That stored water is a precious resource for fish, hydro producers, irrigators and other.


A big snow would be particularly valuable following an El Nino year. The Columbia River basin's water supply for the April-September period, as measured at The Dalles Dam, is only 79 percent of normal, according to the Northwest River Forecast Center's July 8 final forecast.


Bonneville Power Administration meteorologist Chris Karafotias says that the transition from El Nino to La Nino was likely responsible for this spring's surge of moisture and cool weather in the Northwest, which was followed by a brief heat wave. The flip-flopping of weather patterns will continue to make seemingly unpredictable weather more common, at least through next winter, he said


"We see this kind of weather pattern about one every 10 years," Karafotias said. "This summer has also been reminiscent of what we've seen before with a transition between El Nino to La Nina. It typically causes cooler than average temperatures in western Oregon and Washington through October, with the exception of September, which should be warmer than normal. So far, this is playing out as we expected."


Karafotias also expects some wild weather this fall.


"I expect at least two significant weather events as the pattern continues to shift further into La Nina," he said. "I think we'll have a wind storm into the Willamette Valley this fall or early winter, and, if history repeats itself, the wind velocity would exceed 100 miles per hour at the coast. We could also see western Oregon and Washington flooding, based on what has happened in the past with this type of weather pattern."


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