[env-trinity] CBB: 'La Nina' Now Reigns PNW Weather; Colder Ocean Should Be Boost To Basin Salmon Survival

Sari Sommarstrom sari at sisqtel.net
Fri Aug 13 15:59:12 PDT 2010

'La Nina' Now Reigns PNW Weather; Colder Ocean 
Should Be Boost To Basin Salmon Survival

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."

Weekly Fish and Wildlife News
August 13, 2010
Issue No. 541

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