National Oceanic and Atmospheric Administration forecasters are predicting a La Niña winter for California, increasing the potential for warmer and drier weather.

The forecast is based on data collected from tropical Pacific Ocean surface temperatures, ocean currents, and atmospheric winds to calculate the El Niño-Southern Oscillation, which is used to predict whether the upcoming fall and winter will be El Niño, La Niña, or neutral.

In La Niña events, “it’s one of those things where you can go one way or the other, but typically it tilts drier,” said Stephen McCoy, a meteorologist with the National Weather Service in Hanford.

But a La Niña forecast is no guarantee that the winter will be a dry one, he said.

In the winter of 2022-23, “we were actually in a strong La Niña event, which brought heavy, heavy rainfall to the area,” McCoy said. “Typically, we do see drier, warmer conditions with La Niña, but it’s not always the case.”

Drought in the U.S., Valley

According to the latest U.S. Drought Monitor map, there are now only a few pockets of “exceptional” drought (D-4) in the western U.S., and the Valley is divided between “moderate” drought (D-1) on the west side and “abnormally dry” (D-0) on the east side.

It was only three years ago in November 2022 that the entire San Joaquin Valley was mired in the exceptional drought category, which eased with the arrival of record-setting rains that flooded coastal areas and laid a thick, record-setting snowpack atop the Sierra.

Why is the snowpack important? Much of California’s water supply for homes, businesses, and agriculture comes from Sierra snow runoff, which is stored in dams and then released through the state’s extensive canal and piping system.

The winter of 2022-23 brought a series of “freight train” storms with significant precipitation that fortunately took aim at different parts of the state, said Ryan Jacobsen, CEO of the Fresno County Farm Bureau.

What Happens in La Niña

In La Niña winters. the jet stream typically moves to the north, bringing colder and wetter weather to the Pacific Northwest, Jacobsen said.

But, he said, “all it takes is for that jet stream to move a few hundred miles to the south and the outlook completely changes.”

The unpredictability of long-range forecasts was evidenced just in this summer’s forecast for the Valley, McCoy said. After a cool spring, forecasters were preparing for blazing summer temperatures, which in the Valley have been steadily intensifying in recent years.

But the summer turned out to be one of the coolest in decades. It was “almost winter in that we were getting trough after trough after trough” of low-pressure systems rolling in from the ocean, bringing cooler temperatures, McCoy said.

The low-pressure systems helped push eastward the dreaded high-pressure heat dome, which typically parks overhead and brings scorching summer temperatures to the Valley, he said.

What Does This Mean for Farmers?

Are farmers gearing up for shorter water supplies if La Niña means a drier winter? Jacobsen said it’s still too early to make those preparations, but farmers will definitely be watching the skies and hoping for an average or even above-average year for rain and snowfall.

“With the exception of 2024, we came really close, but there is no such thing as average. California, generally speaking, we have enough water, we don’t have enough water. Very rarely do we fall within that middle ground there,” he said.

Westlands Water District, which is the nation’s largest agricultural water district and which supplies water for farmers on the Valley’s westside, said the potential for a dry winter “only underscores the urgent need to ensure our farmers have a guaranteed and reliable water supply year over year so they can continue to feed the nation,” said Elizabeth Jonasson Rosas, deputy general manager of external affairs in an emailed statement. “We cannot depend on Mother Nature alone.”

Westlands farmers have worked hard to be good stewards of their water supplies, preparing for dry years by recharging groundwater sources, she said.

But the aquifer would be best protected if farmers could minimize the need for groundwater pumping, “for which a dependable surface water supply is key,” Jonasson Rosas said. “State and federal leaders must invest in storage, recharge, conveyance, and data-driven management practices that ensure sufficient water is available in both wet and dry years.”