The La Niña expected to shape the West’s winter has strengthened in the past month and almost certainly will stay through at least March, the National Oceanic and Atmospheric Administration said Nov. 11.
Although weak now, the La Niña likely will qualify as a moderate La Niña in December and January at its peak, NOAA’s Climate Prediction Center reported.
A La Niña generally brings cool and wet winters to the Northwest, particularly Washington and northern Oregon. La Niña portends warm and dry winters farther south.
The La Niña could relieve drought in some places and deepen it in others.
The U.S. Drought Monitor reported Nov. 11 that almost the entire West is still in drought or at least abnormally dry. The only exceptions are most of Western Washington — including Pacific County, where annual rainfall is running about 17% ahead of 2020 — and Clatsop and Tillamook counties in Oregon.
Cool sea-surface temperatures along the equatorial Pacific trigger a La Niña. NOAA predicted a 66% chance that temperatures will cool enough to form a moderate La Niña at its peak.
There’s a 14% chance that temperatures will cool to 1.5 degrees Celsius below normal, low enough for a strong La Niña, according to NOAA.
In the past week, sea-surface temperatures in the central Pacific were 1 degree below average, the line between a weak and moderate La Niña.
Pacific Ocean temperatures were last cool enough to form a strong La Niña in the winter of 2010-11. A moderate La Niña formed last winter.