weak La Nina weather pattern is still predicted to settle in before winter, but
that powerful atmospheric influence is unrelated to a “river of moisture” that
is moving across the Pacific Northwest this week.
NOAA Climate Prediction Center put out its monthly outlook Thursday along with
a teleconference from College Park, Md.
long-term forecast favors a wetter-than-average winter across the northern
states, including Columbia Basin states, along with colder-than-average
temperatures. That has been the outlook for the last couple months with a La
Nina in effect — a designation that could be upgraded to an advisory in coming
La Nina conditions develop, we predict it will be weak and potentially
short-lived, but it could still shape the character of the upcoming winter,”
said Mike Halpert, deputy director at the Climate Prediction Center. “Typical
La Nina patterns during winter include above-average precipitation and
colder-than-average temperatures along the northern tier of the U.S. and
below-normal and drier conditions in the South.”
Nina kicked in prior to the winter of 2016-2017, and the result was cold
temperatures and record or near-record snowpacks in Oregon, Washington, Idaho
and Montana, followed by a bountiful runoff in the Columbia River Basin and a
return to hot-and-dry weather in the region after La Nina subsided.
and other NOAA forecasters caution one La Nina or El Nino pattern will differ
from others — in other words, their influences on weather will differ. Weather
can also be greatly affected by other powerful but short-term atmospheric
forces, such as the Arctic Oscillation and “Polar Express” patterns.
“atmospheric river” that stretched across a 5,000-mile region of the Pacific
Ocean this week is unrelated to a La Nina pattern that has yet to become
established, said David Bishop, a meteorologist with the National Weather
Service in Portland.
Nina has a 55-to-60 percent chance of developing before winter sets in,” Bishop
said. “This is a completely independent system.”
noted that the media has become somewhat captivated by atmospheric rivers in
recent years, but “they are not out of the ordinary by any stretch of the
added that “It is, quite literally, a river of moisture in the atmosphere. It
can bring a lot of rain and storm-force winds, which can lead to dangerous surf
conditions on the seaboard.”
images show this week’s event taking shape in a stunning stretch of clouds and
low-pressure pockets stretching from China to Washington and Oregon, prior to
the system swiftly moving to the east.
said two or more inches of rain were expected to fall in western Oregon from
Wednesday evening through late Saturday-early Sunday. The freezing elevation
during that period in the Pacific Northwest was expected to reach a low of
4,000 feet on Friday night and up to 5,000 feet during the duration of the
event. After it subsides, the freezing level is expected to be at elevations
above 8,000 feet.
Also see: http://www.noaa.gov/media-release/us-winter-outlook-noaa-forecasters-predict-cooler-wetter-north-and-warmer-drier-south