Dryer, warmer winter may be on tap
August 25, 2012
A two-year reality of precipitation-rich winters – even more so than normal – in the Pacific Northwest could well be broken if climatic conditions in the equatorial Pacific shift from so-called neutral conditions toward El Nino.

La Nina conditions have prevailed for most of the past two winters. Such cool conditions have more often than not produced wetter and cooler than average conditions in the Pacific Northwest.

El Nino conditions in the south Pacific, on the other hand, tilt the odds toward drier, warmer winters in the Northwest, where moisture laden clouds are the building blocks for the region’s mountain snowpack. Snow meltdown is the largest source of water for the Pacific Northwest’s Columbia/Snake river system.

“ENSO-neutral conditions continued during July 2012 despite above-average sea surface temperatures (SST) across the eastern Pacific Ocean,” according to an August 9 El Nino/Southern Oscillation diagnostic discussion posted online by the National Weather Service’s Climate Prediction Center.

“Although sub-surface and surface temperatures were above average, many aspects of the tropical atmosphere were inconsistent with El Niño conditions,” the report says. “Upper-level and low-level trade winds were near average along the equator, while tropical convection remained enhanced over Indonesia.”

However, convection increased near and just west of the International Date Line, which may eventually reflect a progression towards El Niño.

“Nearly all of the dynamical models favor the onset of El Niño beginning in July-September 2012.

“Supported by model forecasts and the continued warmth across the Pacific Ocean, there is increased confidence for a weak-to-moderate El Niño during the Northern Hemisphere fall and winter 2012-13. El Niño conditions are likely to develop during August or September 2012,” the report says. The discussion is a consolidated effort of the National Oceanic and Atmospheric Administration, NOAA’s National Weather Service, and their funded institutions. Oceanic and atmospheric conditions are updated weekly on the Climate Prediction Center web site

Australian climate experts located close to those equatorial sites also feel an El Nino is in the offing.

“Climate indicators in the tropical Pacific Ocean remain close to El Niño thresholds. Although El Niño development stalled during the second half of July, over the past fortnight indicators such as the Southern Oscillation Index and trade wind strength have shown renewed trends that are consistent with the early stages of an El Niño event,” according to an Aug. 14 update provided by the Australian government’s Bureau of Meteorology.

The Bureau’s web page: http://www.bom.gov.au.

“Likewise, the central Pacific Ocean has continued to warm. Climate models surveyed by the Bureau of Meteorology continue to show further warming across the tropical Pacific Ocean, with temperatures exceeding El Niño thresholds before the end of September 2012. None of the models surveyed indicate a return to La Niña conditions,” according to the Australian bureau, which updates its El Nino/Southern Oscillation Index assessment’s every two weeks.

Researcher Nathan Mantua of the University of Washington’s Climate Impacts Group says the jury is still out on whether El Nino will get a grip on global weather, or if ENSO neutral conditions will prevail. Neutral conditions generally are viewed as leaving an equal chance of above, below or average precipitation and temperature conditions.

It’s usually not until August or September when the trend “starts to become clear,” Mantua said.

“We’ve had a string of cool phase months since 2010,” and mostly since 2007, Mantua said of the longer term climatic trend sometimes described as the Pacific Decadal Oscillation. That cool phase, which was interrupted in the winter of 2009-2010, could muffle ENSO effects.

“This year I’m not sold” that El Nino will hold sway, Mantua said. “I think that the forecasts I look at suggest that the highest likelihood is that it may be weak El Nino.”

What is apparent is that La Nina looks to be very unlikely for this winter.

“So at least from that piece of information you can downgrade the odds for having another winter/spring like the past two,” said Mantua. Those past two years witnessed wetter and cooler than normal conditions across most of the Northwest that stretched well into the spring.

The prospects for young salmon and steelhead leaving the Columbia River and entering nearshore Pacific Ocean have been good during those past two years, according to Bill Peterson of NOAA Fisheries’ Northwest Fisheries Science Center.

La Niña conditions had weakened as of early summer, according to a June update of the NWFSC’s long-running research, “Ocean Ecosystem Indicators of Salmon Marine Survival in the Northern California Current.”

But, similar to 2011, 2012 got off to a promising start in terms of cold La Niña conditions and higher than average abundances of northern copepods, a healthy foundation of the food chain.

“… despite the predictions for potential ENSO-neutral or El Niño-like conditions developing during the second half of the year in equatorial waters, we expect the favorable biological conditions to persist through the summer as they typically lag changes in physical parameters by 3-6 months."