National Oceanic and
Atmospheric Administration
La Niña causes the jet stream to
move northward and to weaken
over the eastern Pacifi c.
The
Illahee
Apartments
Weather patterns
to look for in a La Niña year
BY REBECCA LEXA
As good as it gets
in Downtown
Astoria!
1046 Grand Avenue
Astoria, OR 97103
503-325-2280
4 // COASTWEEKEND.COM
Winter arrived in the Colum-
bia-Pacifi c region with a blast of cold
air and a few inches of snow that
just skirted the end of Christmas. It’s
unusual weather here. But it’s not
uncommon as part of the La Niña
portion of the ENSO phenomenon,
and we are in a La Niña year.
ENSO stands for El Niño-South-
ern Oscillation, which is a shifting in
water temperatures in the eastern half
of the Pacifi c Ocean’s tropical region,
off shore from Ecuador, Colombia and
Peru. The phenomenon begins with
the Walker circulation, an air fl ow
pattern in the equatorial Pacifi c that
aff ects air pressure and temperatures.
During an average year, this circu-
lation maintains high pressure over
the eastern equatorial Pacifi c Ocean,
and low pressure to the west. The
high pressure feeds the trade winds,
which draw cold, deep water from the
ocean to the surface, cooling air over
the ocean. That cool air then travels
eastward, aff ecting temperatures and
weather patterns across the Americas.
During a La Niña year, extra-
high pressure builds over the eastern
Pacifi c, reducing water temperatures
and, by extension, bringing in cooler
air over the water. Conversely, in an
El Niño year, the Walker circulation is
either much weaker, or even reversed;
the trade winds slow, and less cold
water is added to the ocean’s surface,
warming water and surrounding air.
Both of these changes can bring dra-
matic eff ects to weather patterns, even
those thousands of miles to the east.
Diff erent parts of the country have
diff erent La Niña eff ects, at least
based on what we’ve seen over the
past century. Like us, the region south
of the Great Lakes tends to be wet-
ter, the southern third of the country
is likely to be drier, and the South-
east in particular is warmer during
La Niña. And the northern Great
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