Bay Area weather: No rain forecast through Christmas Eve

An atmospheric river came roaring off the Pacific Ocean on Monday, bringing heavy rain and days of expected downpours. But it only hit Washington and Oregon, missing California entirely.

After a promising, soaking start to the winter season with multiple storms in mid-November, the state suddenly is coming up dry.

Umbrellas have given way to sunny skies, with no end in sight. Through Monday, the Bay Area has received no rain for 18 days in a row since a quarter-inch fell on Nov. 20. And the long-range forecast is showing more of the same: another 16 days of dry conditions through at least Christmas Eve.

If that plays out, the Bay Area would have 34 days in a row of dry weather — making it the seventh-longest dry spell starting in November or December in recorded history back to the Gold Rush in 1849. The last time there were more consecutive dry days during the start of winter was in 2014, during California’s withering five-year drought. Before that, it was in 1989 and 1976.

“We had a really wet November,” said Jan Null, a meteorologist with Golden Gate Weather Services in Half Moon Bay. “We were above normal early on. Now it’s possible we could go 0-for-December. It’s been feast or famine.”

Those dry conditions also have hit the Sierra Nevada, putting a serious crimp in the beginning of ski season. On Monday, the statewide Sierra Nevada snowpack was just 25% of its historical average, with the Northern Sierra at just 7%.

Although some Tahoe-area ski resorts have opened with lots of artificial snow, others have not yet.

“Some years you get an early winter and good momentum going into the holidays,” said John Rice, president of Ski California, an industry association. “Sometimes its a little slower. Mother Nature is a little late to the game this year.”

So should Californians start worrying about a drought?

No, experts said Monday.

“It’s still early,” said Jay Lund, a professor of civil and environmental engineering at the University of California, Davis. “If this was a baseball game we’d be in the second inning.”

Null, a former lead forecaster with the National Weather Service who compiled much of the data, noted that on average the Bay Area receives 59% of its yearly rainfall in just three months: December, January and February. Even if December is a bust, he said, November was wet and the region can catch up in January, February, and also possibly March.

“Historically, there is very little correlation between what we get early in the season and what we end up with at the end of the season,” Null said. “This dry month doesn’t mean we are guaranteed a dry year.”

On Monday, San Francisco’s rain total since Oct. 1 had dropped to 78% of its historical average for that date. Oakland was at 107% and San Jose, which got the brunt of several mid-November storms, was at 174%, all of them dropping several percent with each day that passed without any new rain.

In the Tahoe area, ski resorts like Mount Rose, Heavenly and Northstar have opened, their snow-making machines cranking, Rice said. Others, such as Palisades, have opened just for kids lessons, while Kirkwood opened this past weekend, and Tahoe-at-Donner expecting to open Dec. 19.

“They all should be open by Christmas,” Rice said. “It’s going to snow. It always does. It’s just a matter of when. I thought I was causing the problem because I was checking the weather forecast so often. We’re dressed up, we’re ready for the party. The minute it snows the resorts are going to take off.”

Even though California’s rainy season is generally considered to run from Oct. 1 to May 1, the first day of actual winter isn’t for nearly two weeks, until Dec. 21.

“So far, it is looking that December will likely turn out to be a drier- and warmer-than-average month for most of California,” wrote Daniel Swain, a climate scientist with the University of California, on his weather blog Friday. “We’ll see what the rest of the season holds. But the winter is mostly still in the future tense!”

Another promising tidbit: For the first time in 25 years, the last three winters in California have seen average or above average precipitation. The most recent drought ended in 2022.

As a result, the state has hydrologic “money in the bank” with healthy reservoir levels, and even groundwater levels that have risen in many places, including Santa Clara County, where groundwater makes up nearly half of the drinking water supply.

On Monday, the state’s largest reservoir, Shasta, near Redding, was 59% full, or 108% of its historical average for that date. The second largest, Oroville, in Butte County, was 51% full, or 98% of its historical average. San Luis Reservoir, east of Gilroy, was 63% full, or 117% of normal. And farther south, the largest reservoir in Southern California, Diamond Valley in Riverside County, was 94% full, or 135% of normal.

“The reservoirs are pretty full for this time of year,” Lund said. “We wouldn’t want them to be much fuller or we’d be worried about floods.”

What has caused all the dry weather?

A persistent ridge of high pressure over the West Coast has blocked storms from hitting California, pushing them north to the Pacific Northwest, Null said. That same ridge is causing winter havoc in the East Coast, by sending storms up into Canada, where they absorb cold air before dropping back down into the United States as blizzards.

Over the three major droughts that California has suffered since 2007, similar high-pressure ridges were a big part of the reason for the lack of rain. When the current ridge will break down, nobody knows, Null said.

But for now, given the amount of water stored up, and the months of winter still ahead, the current dry spell should be enjoyed, not feared, he said.

“Even if it stays dry, one dry year isn’t cause for concern,” Null said. “It’s too early to even have that conversation. In most parts of the state we don’t start to have drought problems until two or more dry years in a row.”

Lund agreed.

“Don’t panic,” he said. “Stay tuned.”