La Niña: Is California heading into another dry winter?

Paul Rogers, Mercury News on

Published in Weather News

SAN JOSE, Calif. — You may have seen it on social media or heard it while talking to a friend: This is a La Niña year, so California won't get any rain this winter and the severe drought is only going to get worse. Right?

Maybe not. Although that's a common belief, it's not supported by past history. The reality is that a lot depends on where you live.

"The message most people get about La Niña seems to be biased by Southern California," said Jan Null, a meteorologist with Golden Gate Weather Services in Half Moon Bay. "There is a really good connection between La Niña and drier-than-normal weather in Southern California. But in Northern California, it's a coin flip."

La Niña conditions occur when Pacific Ocean waters off South America are cooler than normal. They are the opposite of El Niño, the atmospheric trend when waters there are warmer than average.

Null, a former lead forecaster with the National Weather Service, has spent years tracking the amount of rainfall California receives every winter and looking for trends.

Since 1950, there have been 23 winters with La Niña conditions, his records show. Although some were dry, like last year or 1976-77, some also were very wet, such as the winter of 2016-17, when relentless atmospheric river storms caused the near-failure of Oroville Dam. Rainfall that winter ended the state's previous drought and prompted widespread flooding in downtown San Jose.


The average rainfall over those 23 years was 93% of normal.

Similarly, the region farther north, where California's largest reservoirs are located, including Shasta, Oroville, Trinity and Folsom, has received 97% of normal rainfall, on average, in La Niña years. And the rugged coast near the California-Oregon border has received an average of 103% of normal rainfall during La Niña years.

So why does the stubborn belief persist that La Niña guarantees dry weather? The farther south one goes, the drier it has been in La Niña years.

Null's data shows that La Niña years have brought only 79% of normal rainfall, on average, to the Los Angeles-San Diego area.


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