Winter precip far below normal
|
|
December 21, 2013 |
A late summer deluge soaked the Pacific
Northwest, but precipitation has been
considerably less than recent decades’ average
ever since as the region heads into what is its
all-important wintertime snow/water supply
accumulation period, according to latest issue
of the PNW Climate Impacts and Outlook produced
by the Climate Impacts Resource Consortium.
And most sources say that predictions of
near-term future precipitation are made more
difficult because El Nino/Southern Oscillation
signs are in a neutral phase.
“The majority of atmospheric and oceanic
indicators used to monitor ENSO are well within
the neutral range,” according to the December 17
ENSO update released by Australia’s Bureau of
Meteorology. International climate models
surveyed by the Bureau of Meteorology indicate
the tropical Pacific is expected to remain
neutral at least through to the first quarter of
2014.
ENSO is the major source of inter-annual climate
variability in the Pacific Northwest, according
to the University of Washington’s Climate
Impacts Group. ENSO variations are more commonly
known as El Niño (the warm phase of ENSO) or La
Niña (the cool phase of ENSO).
An El Niño is characterized by stronger than
average sea surface temperatures in the central
and eastern equatorial Pacific Ocean, reduced
strength of the easterly trade winds in the
Tropical Pacific, and an eastward shift in the
region of intense tropical rainfall.
A La Niña is characterized by the opposite –
cooler than average sea surface temperatures,
stronger than normal easterly trade winds, and a
westward shift in the region of intense tropical
rainfall. Average years, i.e., years where there
is no statistically significant deviation from
average conditions at the equator, are called
ENSO-neutral
El Niño winters tend to be warmer and drier than
average with below normal snowpack and
streamflow, according to CIG.
La Niña winters seem to tilt the odds toward
cooler and wetter than average winters with
above normal snowpack and streamflow.
Similar to precipitation, there are equal
chances of above, below, or normal temperatures
across the Pacific Northwest, as estimated in
the most recent NOAA’s Climate Prediction
Center’s three-month forecast. That
December-February forecast is for a slightly
higher than equal chance for above average
precipitation during the period across much of
Montana.
The CPC winter “outlook” for the United States
can be found at:
http://www.noaanews.noaa.gov/stories2013/20131121_winteroutlook.html.
September 2013 was the wettest on record in the
Pacific Northwest (Oregon, Washington, and
Idaho), with a regional average of 3.68 inches
(2.47 inches above the 20th century average). In
late September, remnants of Typhoon Pabuk soaked
western Oregon and Washington, according to the
CIRC newsletter.
A ridge built into the region, making for an
abnormally dry start to the water year, which
runs from October 1 to September 30, especially
in southern Oregon, the Snake River Valley, and
eastern Washington’s Palouse. October to
November 2013 was the 12th driest such period on
record, according to the CIRC.
The regionally averaged total of 3.18 inches was
2.70 inches below the 20th century average, and
the driest since 2002.
According to the NOAA National Weather Service’s
Northwest River Forecast Center, precipitation
in the area upstream of the lower Snake’s Ice
Harbor Dam was only 49 percent of its average
for this month through December 16.
Precipitation in that Snake River part of the
Columbia basin was 38 percent of average in
October and 48 percent of average in November.
Upper Columbia precipitation – above central
Washington’s Grand Coulee Dam – was also low at
70 percent of average during the first 16 days
of December, following 24 percent of average in
October and 86 percent of average in November.
The area upstream of the lower Columbia’s The
Dalles Dam, which includes the Snake and mid and
upper Columbia, was 57 percent of average
December 1 to 16; 30 percent of average in
October and 63 percent of average in November.
The NWRFC’s first official water supply forecast
for next spring and summer is scheduled for
release in early January.
The Pacific Northwest Climate Impacts Research
Consortium delivers science, information, and
tools to decision makers responsible for the
management of resources and services in a
changing climate. It is housed in the Oregon
Climate Change Research Institute at Oregon
State University. The team consists of experts
from Oregon State University, the University of
Oregon, the University of Idaho, Boise State
University, and the University of Washington.
CIRC is funded by the National Oceanic and
Atmospheric Administration..
You can find the latest issue of the PNW Climate
Impacts and Outlook on the new CIRC website:
http://pnwcirc.org/wp-content/uploads/2013/12/circfall_final.pdf. |
|
Questions or comments about this
article?
Click here to e-mail! |
|
|
|
|
