La Niña has arrived, with little rain in store for Southern California

La Niña has officially arrived, with mixed messages for California.

If the weather phenomenon behaves as expected, the Pacific Northwest and far Northern California will enjoy a wetter than normal winter, while the southern swath of the state will remain dry.

Federal climate scientists on Thursday declared La Niña conditions, saying they lacked strength and would probably last only a few months.

“The weak La Niña is likely to contribute to persisting or developing drought across much of the southern U.S. this winter," said Mike Halpert, deputy director of the Climate Prediction Center at the National Oceanic and Atmospheric Administration.

Characterized by a cooling of sea surface temperatures in the equatorial Pacific, La Niña triggers atmospheric changes that generally favor below-average precipitation and above-average temperatures in the country’s southern band. That is bad news for the Southland, which missed out on last winter’s El Niño rains that eased the drought in much of California.

On the bright side, NOAA’s La Niña map shows the area of above-average precipitation reaching down into far Northern California, into watersheds that feed the state’s largest reservoirs.

And the rainy season has gotten off to a good start in the northern Sierra Nevada, where precipitation is 250% of average for the date. In the Central Sierra, it is 180% of the norm.

Last week, the U.S. Drought Monitor reported that a rainy October in Northern California had lifted about a quarter of the state out of drought conditions, the best picture since the spring of 2013. Still, much of Central and Southern California remains locked in what the drought monitor called "exceptional or extreme drought."

La Niña has developed on the heels of one of the strongest El Niños on record, which helped recharge California’s dangerously low reservoirs but failed to live up to predictions of blockbuster storms.

bettina.boxall@latimes.com

Twitter: @boxall

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