Storms may hamper holiday travel plans

“The next storm will likely be colder, with more limited moisture.” Christopher Castellano, a meteorologist at Scripps Institute

of Oceanography

A parade of winter storms will greet Californians for the holiday season, with active weather up and down the Golden State expected for the final two weeks of 2023.

The next seven days will be the wettest since at least March in the Bay Area and Sacramento Valley, while Southern California could pick up its most rain since Tropical Storm Hilary in August. Low-pressure systems, including an atmospheric river, are expected to bring rounds of heavy rain to California between Sunday afternoon and Friday morning, with 2 to 5 inches of rain possible between San Francisco and Santa Barbara.

Central and Northern California will take the brunt of the storms Sunday, Monday and Tuesday, while impacts are expected to stretch statewide Wednesday and Thursday. No river flooding is forecast, but urban roadways and small streams could be overwhelmed by heavier downpours.

A brief break in the wet weather is possible Friday afternoon through Christmas Eve, but there is a strong signal that stormy weather — possibly hazardous in some areas — will return on Christmas Day and continue through the end of the year.

Atmospheric rivers return

Last winter, several atmospheric rivers made landfall in the Bay Area, unleashing torrential downpours and widespread flooding. Atmospheric river storms have impacted the Pacific Northwest and Northern California this winter, but they have largely run out of moisture before reaching the Bay Area.

That’s expected to change this week, though, as an atmospheric river interacts with a strong storm system in the Pacific Ocean, pushing humid air toward the Bay Area. This humid, tropical air will bring with it some unsettled weather, including the chance of lightning and heavy downpours along the Peninsula on Sunday night.

From Sunday afternoon through Tuesday, San Francisco, Oakland and Sacramento can expect 2 to 3 inches of rain. The storm’s tropical influence and warmer air will push the snow line above 8,000 feet Monday and Tuesday before dropping below 6,500 feet Wednesday.

Higher rainfall amounts are expected early next week in Santa Cruz, the North Bay and along the North Coast, with less rain in the Santa Clara and San Joaquin valleys. Only light precipitation amounts are anticipated south of Santa Barbara on Monday and Tuesday. Gusty winds along the coast are also possible, especially Monday.

“We could be gusting out of the south into the 30- to 45-mph range in some spots,” said Brian Garcia, a meteorologist at the National Weather Service. “That’s something we have to watch. … Could have some branches down, trees down and potential power outages.”

The Scripps Institute of Oceanography at UC San Diego, which created an atmospheric river scale from 1 to 5, forecasts next week’s storm as a category 3, with a “balance of beneficial and hazardous” conditions. The Weather Prediction Center forecasts a slight risk of flash flooding in the Bay Area on Sunday and Monday, with low-lying urban areas and small streams at highest risk.

Tuesday afternoon may serve as a brief break in the heaviest rain before another storm takes aim at Central and Southern California from Wednesday morning through midday Friday. San Francisco, Los Angeles and San Diego are likely to receive widespread heavy rain from this system. Accumulations from the second storm are expected to range between 1 to 3.5 inches along the coast, but forecast details are still emerging.

“The next storm will likely be colder, with more limited moisture,” said Christopher Castellano, a meteorologist at Scripps. “So less tropical moisture will make its way to California. Also, a greater potential for accumulating snowfall below 8,000 feet in Sierra Nevada.”

Christmas storms

Quieter weather is expected for pre-Christmas travel Dec. 23 and 24, but another stormy weather pattern is on the horizon between Christmas Day and New Year’s Eve.

An extremely active Pacific jet stream will raise the odds for atmospheric rivers, wind storms and potentially blizzardlike weather in the Sierra Nevada for the final week of December. Timing and exact impacts of the weather pattern are uncertain, but the Climate Prediction Center highlights California for a number of hazards from December 25-28.

The most significant Sierra snowfall of the season is possible as Pacific moisture encounters colder air over the mountains. Several feet of snow are needed in the Sierra Nevada, which is in a snow drought so far this winter.

The start to this winter’s active weather has shades of last year, when a stormy holiday weather pattern followed an abnormally dry fall. It’s too early to say whether this level of activity will continue into early 2024, but with a strong El Niño in place, it’s more likely than not that Central and Southern California will have a wetter than normal winter.