Third year of La Niña on tap this winter, according to official forecast

The National Weather Service Climate Prediction Center issued its official winter outlook Thursday, and, as expected, a third year of La Niña appear to be on tap.

That means continued, deepening drought likely in Southern California and the southwestern United States, even expanding across the southern states into the Gulf Coast and much of the Southeast, meteorologists say.

But while La Niña atmospheric conditions have meant major drought for Sonoma County and the Bay Area since 2020, its impact on the region in the coming months remains unclear — an acknowledged frustration for those seeking greater certainty.

Positioned between the Pacific Northwest, where wetter than normal conditions are anticipated, and the southwest, where drought is expected to dominate, most of Northern California has equal chances of falling into either camp or something closer to average, said Jon Gottschalck, chief of the Climate Prediction Center’s Operational Prediction Branch, who spoke during a virtual news conference Thursday.

“You could almost describe it as a flip of a coin,” Sonoma Water General Manager Grant Davis said in a separate interview.

The same is true across a large band of the United States, including most of Nevada, Utah, Colorado, Nebraska, Iowa and Missouri, which are among the states that have “equal chances for below, near or above average precipitation,” Gottschalck told reporters.

The stretch of coastline from the Bay Area to southern Oregon has especially high variability, Gottschalk said. Rainfall is more often determined by sub-seasonal climate events like atmospheric rivers or areas of high pressure that last three weeks, rather than some longer term pattern like La Niña.

And if a high pressure ridge should set up, a subtle shift in the ridge or a low pressure trough could mean a significant change in whether rain drenches a large chunk of California or it stays dry, he said.

It’s very hard to predict over even a few weeks, Gottschalk said, “let alone over a whole season.”

In an effort to try to break loose funding to work on greater predictability for West Coast conditions, a coalition of water managers from Western states this week urged federal legislators to get behind their efforts, said Davis, who was part of a delegation visiting Senate offices in Washington Thursday.

The Western States Water Council, launched in 2017, is seeking $15 million a year for the National Weather Service to improve modeling and research on West Coast issues like atmospheric rivers — the moisture-laden plumes that provide most of the water supply for Sonoma County and neighboring areas.

Funding for the National Weather Service is biased toward Eastern states and the Atlantic, focused on predicting hurricanes, tornadoes and blustery Nor’easters, without the same attention going to the other side of the country, Davis said.

The region’s sub-seasonal variability begs for greater forecasting acuity, Davis said.

“Right now, a flip of the coin doesn’t help us one bit,” he said.

There’s about $1 million in the Senate appropriations bill right now — a place to start, Davis said. But for those trying to manage limited water supply and drought fatigue, planning without a clear direction is awfully tough.

Meteorologists say they are particularly confident La Niña conditions will prevail from December through February of next year, meaning currents circulating in the Pacific Ocean have churned up cold surface water in the eastern part of the ocean, with a transition to a weaker signal after that.

It will be the third successive La Niña, sometimes called a “triple-dip” — the third triple-dip since 1950, the beginning of the El Niño-Southern Oscillation historical record. The two prior stretches were 1973—1976 and 1998—2001.

Though Sonoma County has had below seasonal rainfall for three consecutive years, last winter was brought more than the two previous seasons, with 27.13 inches measured at the Charles M. Schulz-Sonoma County Airport from Oct. 1, 2021 to Sept. 30, 2022.

There were 19.35 inches of rain at the airport in the 2019-20 water year and 13.01 inches in 2020-21. Normal is 33.78 inches, the National Weather Service said.

Lakes Sonoma and Mendocino are each holding less than 44% of their total capacity, though a seasonal curve used to measure storage in the smaller, northern reservoir puts current storage closer to 66%.

Davis said local consumers have demonstrated their ability to conserve water if they need to through another dry winter after reducing consumption enough for the water agency to draw 30% less than usual from the Russian River watershed last year.

“We are capable of pulling back and making it through,” he said.

You can reach Staff Writer Mary Callahan (she/her) at 707-521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.