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Dryer, warmer winter may be on tap
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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." |
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