The day before the state’s “water year” ended, Silicon Valley leaders gathered on Google’s campus in Mountain View and urged residents to continue conserving water as California’s drought drags on.

“It’s the third straight year of a bad and worsening drought,” said Wade Crowfoot, secretary of the California Natural Resources Agency, on Thursday. “Our scientists and climatologists predict that as we move into the winter, we can expect another, fourth dry year.”

Not exactly, say experts.

“Those are the kinds of statements that make me grind my teeth,” said meteorologist Jan Null, a former lead forecaster with the National Weather Service.

First, nobody can predict the weather with any accuracy beyond 10 days, Null notes. Second, although there are La Niña conditions now — where surface waters in the Pacific Ocean are cooler than normal along the equator — the commonly held belief that La Niña automatically means dry winters for California isn’t supported by the historical record.

Since 1950, there have been 24 winters with La Niña conditions, according to Null’s detailed studies.

Although some were dry in California, such as the past two years or the winter of 1976-77, some also were very wet, such as the winter of 2016-17 when relentless atmospheric river storms filled reservoirs, caused the near-failure of Oroville Dam and led to flooding in downtown San Jose.

The average rainfall in the Bay Area during those 24 La Niña years was 93% of normal. Farther north, from the Sonoma coast to the Oregon border, rainfall has been 102% of the historical average during La Niña years and 97% of normal in North-Central California where the state’s largest reservoirs — Shasta, Oroville, Trinity — are located.

“In Northern and Central California, it’s close to a coin toss,” said Null, who now runs Golden Gate Weather Services in Half Moon Bay.

But the story is a little different in Southern California.

Null’s data shows that La Niña years have brought only 80% of normal rainfall on average to the Los Angeles-San Diego area. So the odds are slightly better than La Niña winters such as the one coming up will be drier than normal there.

Other experts agree.

“Southern California is the only place in California that has anything resembling statistically significant drier-than-normal outcomes,” said Michael Anderson, climatologist with the state Department of Water Resources. “The range in Northern California is all over the map.”

“We have it in our heads that El Niño means wet, and so the opposite is La Niña, and the opposite is dry. But the reality is not all El Niños are super wet, and not all La Niñas are dry.”

On Friday, the state’s “water year” ended. Many water managers and meteorologists use Oct. 1 to Sept. 30 as a 12-month period to measure rainfall because California gets most of its rain during the winter, when one calendar year ends and another begins.

This past “water year” has actually been the best, in terms of total precipitation, of the past three years since the latest drought began.

San Francisco received 84% of its historical average rainfall over the past 12 months. Oakland fared better with 93%. Los Angeles had 88% of normal. San Jose lagged with 58%.

And the Northern Sierra Index, a collection of eight weather stations in the watersheds of major reservoirs such as Shasta Lake, had 81% of normal.

Not bad, right?

The problem is that if California’s weather was a student, this year, it brought home a B-minus average. But the past two years were an F and a D. Cumulatively, the state is in a major precipitation deficit.

“This year was gangbusters better than the last two,” Anderson said. “But it was still overall below average.”

Over the past three years, San Francisco has received just 58% of its total average precipitation, San Jose 50%, the Northern Sierra 62%, with other places showing similar numbers. Overall, most parts of California are missing an entire year’s worth of precipitation since 2020.

Anderson noted that climate change is causing hotter temperatures, like the heat wave three weeks ago, that dry out soils and vegetation, increasing fire risk. During that extreme heat wave, temperatures exceeded 110 degrees across the state. In Livermore, the mercury hit 116, an all-time record for any city on any day in Bay Area history.

And the cumulative effect of the current drought is setting wider records.

The three-year period that ended Friday is the driest three-year stretch California ever recorded since modern weather records began in 1895, according to data compiled by the Desert Research Institute, a branch of the University of Nevada, from dozens of weather stations across the state.

How dry has it been? Statewide, an average of 46.05 inches of precipitation fell during the last three years in California. That’s less than the prior records, which ended in 2015 (49.26 inches) and 2014 (49.53 inches) — the depths of California’s last drought — and the three years ending in 1931 (50.79 inches), during the Dust Bowl.

It did rain and snow a lot last October and December. But then January, February and March were parched.

As a result, reservoirs weren’t refilled. The state’s largest, Shasta Lake, near Redding, was just 33% full on Friday. The second-largest, Oroville, in Butte County, was 35% full. Folsom, near Sacramento, was 36% full.

Previous severe droughts have ended in big, wet winters, like 2017 and 1978, that filled reservoirs in a few months.

Whether that will happen now, nobody knows. Anderson said La Niña conditions are expected to wane by December or January, which might cause an atmospheric shift that could move high-pressure ridges in the Pacific. If there were atmospheric river storms around, some could break through and soak California.

“Something interesting could happen,” he said. “The question is will it? A lot of things have to line up.”