Up to 15 inches of precipitation could fall along the North Coast and other parts of Northern California in the next week.
A series of atmospheric rivers is expected to drench Northern California and the Pacific Northwest beginning this weekend and lasting through the end of next week, potentially disrupting holiday travel and increasing flood risks.
A large area of low pressure in the northeastern Pacific is driving atmospheric river pulses, one after another, into the U.S. West Coast, said Chad Hecht, a research meteorologist with the Center for Western Weather and Water Extremes at the Scripps Institution of Oceanography.
Upward of 15 inches of precipitation could fall along the North Coast and other parts of Northern California over the next seven days. The Olympic Peninsula of Washington and the high elevations of the Cascades will rack up similar precipitation totals. At least five separate atmospheric rivers are forecast, with varying impacts along different parts of the West Coast. There is still uncertainty, however, in the exact timing, magnitude and duration of atmospheric rivers as well as precipitation amounts, according to the Center for Western Weather and Water Extremes.
"As we step our way through each storm, they are going to make their way down the coast, shifting the focus to California," Hecht said.
While each individual storm may not be extreme, atmospheric rivers that strike in close succession often boost the risk of serious flooding. Creeks, streams or rivers could flood if there is not enough time for water levels to recede between storms.
Although storms moving through this weekend are expected to bring beneficial rain, more severe impacts could arrive next week.
A strong system is forecast to make landfall on Monday and bring rain to coastal Washington, Oregon and Northern California into Tuesday. Another robust system could follow closely on its heels beginning late in the week.
The storms will initially be warm but could still deliver significant mountain snow.
"Higher elevations are going to get a lot of snow," Hecht said. "It will be a wet, heavy type of snow -- Sierra cement versus light, fluffy snow."
The National Weather Service office for San Francisco is also warning of "life-threatening bay, ocean and beach conditions" beginning Saturday. Dangerous surf and large breaking waves up to 30 feet are possible along the Northern California and Oregon coasts -- a risk that intensifies next week.
"A very large and powerful, long-period west swell train will likely arrive along our entire coastline Monday into Tuesday next week. ... This will lead to much higher breakers including localized coastal flooding impacts," the Weather Service wrote.
Hecht said that meteorologically, this family of atmospheric rivers is very similar to the series of atmospheric rivers that struck California in December 2022 and January 2023, though they are focused farther north and may not necessarily have the same level of serious impacts.
A pattern of wet conditions in the region
The latest round of storms will continue a pattern that has brought wet conditions to the Pacific Northwest and unusually dry conditions to the Southwest since the wet season began on Oct. 1.
That's a classic signature of La Niña, the climate pattern marked by cooler-than-normal water in the tropical eastern Pacific and that has been developing over the last several months.
The wet-dry divide is especially pronounced in California, but the conditions seem to exceed even what's expected in a typical La Niña pattern.
UCLA climate scientist Daniel Swain called the contrast between a wet Northern California and a dry Southern California "genuinely remarkable" and potentially record-breaking.
"There are pockets of Sonoma County that are still on track to experience their wettest start to the Water Year on record -- and wider swaths of [Southern California] that are on track to meet or tie the records for their driest start to the Water Year on record," he wrote in a blog post Thursday.