Californians should brace for flooding and possible landslides, as “heavy to excessive rainfall” is expected over the weekend and into next week, forecasters warned Saturday.
With recovery efforts continuing in parts of the state that were battered by storms earlier this week, the National Weather Service said in a bulletin that a couple of Pacific storm systems were forecast to hit the West this weekend, “bringing heavy lower elevation rain, significant mountain snow, and strong winds.”
The first system would approach the coast on Saturday and move inland, the bulletin said, adding that there were “multiple slight risks of excessive rainfall” that could lead to localized instances of “urban and small stream flooding as well as mudslides.”
“More moderate rainfall will continue into Sunday ahead of a second storm system approaching the coast early Monday morning,” according to the bulletin.
The highest elevations of the Sierra Nevada Mountains were expected to see 3 to 6 feet of snow through Monday, forecasters said. Sierra foothills could see 2 to 3 inches of rain, leading to the possibility of mudslides and flooding, they said.
More than 22,000 California utility customers were without power Saturday evening, according to poweroutage.us. A vast majority were connected to Pacific Gas & Electric, which serves a wide swath of the state from the northern end of Southern California almost to its border with Oregon.
On Saturday, the White House announced President Joe Biden approved a disaster declaration for California that focuses federal aid on three hard-hit counties: Merced, Sacramento and Santa Cruz.
The declaration, which could be expanded to cover additional areas, addresses federal help for recovery and damage from storms dating back to Dec. 27, according to a White House statement.
Assistance will also be available statewide for “hazard mitigation” aimed at softening the affects of future severe weather, it said.
The Golden State has been walloped by a series of storms since late December, leaving at least 21 people dead, according to an NBC News tally.
Authorities spent the week searching for 5-year-old Kyle Doan, who was reported missing Monday after raging floodwater swept him away near San Miguel.
The San Luis Obispo County Sheriff’s Office tweeted that operations had to be suspended again Saturday because of rising water levels and water conditions. The decision to continue searching for Kyle “will be made on a day-by-day basis” when conditions allow, the office said.
There have been some breaks in the storm, giving residents time to assess the damage, but there is more rain to come, Gov. Gavin Newsom said on Saturday during a visit to Merced County, which has been heavily affected by the storms.
“The reality is this is just the eighth of what we anticipate will be nine atmospheric rivers,” he said. “We’re not done.”
Atmospheric rivers, a term coined by a pair of MIT scientists in 1994, are streams of water vapor that can be up to 500 miles wide and as long as 2,000 miles. They carry an estimated 25 times the water equivalent of the Mississippi River 10,000 feet above earth.
"By some estimates, 20 to 25 trillion gallons of water falling over the course of the last 16, 17 days is stacking these atmospheric rivers, the likes of which we've not experienced in our lifetimes," Newsom said.
The governor blamed climate change, which has boosted weather extremes, including intense storms, while raising the temperature slightly but crucially across the state. He said earth scientists probing the impact of global warming have long predicted such extreme and deadly winter weather.
"None of this is a surprise," Newsom said.
The number of atmospheric rivers to hit California in recent weeks hasn’t been finalized, and some of the storms may end up being counted differently, according to National Weather Service meteorologist Ryan Kittell.
The National Weather Service issued a flood warning Saturday for parts of the Sacramento River, where the Tehama Bridge reached flood stage and Ord Ferry was expected to rise above flood stage in the late evening.
The Bay Area’s iconic Golden Gate Bridge was closed for at least an hour Saturday night after a big rig with what was believed to be a contractor’s payload of U.S. mail tipped over shortly after 5 p.m., California Highway Patrol Officer Darrel Horner said.
Storm-related wind was believed to be the cause of the big-rig’s fall. Horner said, “At the time the truck was blown over, the winds were up to about 75 mph. That played a role.”
Minor injuries were reported, and no one was arrested. The tractor-trailer had to be pulled upright and removed from the roadway before lanes could be reopened, he said.
The reopening was announced at 8:12 p.m., a little more than an hour after notice of its closure.
The National Weather Service office that serves the Bay Area said the night could include “brief heavy rain, small hail and gusty winds.”
Parts of Monterey and Santa Cruz counties were under mandatory evacuation Saturday night, authorities in both jurisdictions said. The orders covered flood-prone, low-lying areas.
A road collapsed Saturday in a heap of blacktop near the coastal town of Pescadero, south of Half Moon Bay, officials said.
Newsom, and other state and federal officials have pleaded with residents to “be vigilant” and avoid complacency as the latest weather systems approached.
“I know how fatigued you all are,” Newsom said in a speech during a visit Friday to the coastal enclave of Montecito in Santa Barbara County that was evacuated earlier this week.
“Just maintain a little more vigilance over the course of the next weekend,” he said.
His visit came on the fifth anniversary of the mudslide that killed 23 people and destroyed more than 100 homes in the upscale community.
Speaking in Merced County on Saturday, Newsom thanked members of the California National Guard for clearing out a catch basin that was constructed after the mudslide to divert rain. He asked people to use “common sense” and obey guidance from law enforcement officials.
Nancy Ward, the director of the California Governor’s Office of Emergency Services, echoed Newsom’s message and urged people to remain cautious.
“People will become complacent, but the ground is saturated. It is extremely, extremely dangerous,” Ward said at a press briefing. “And that water can continue to rise well after the storms have passed.”
Damage assessments from the recent storms, which have already started, were expected to surpass $1 billion after roofs were blown off homes, cars were submerged and trees uprooted in parts of the state.
In Southern California, authorities determined that a storm-related sewage spill into the Ventura River was much bigger than initially believed. Two Ojai Valley Sanitary District sewer lines damaged on Jan. 9 spilled more than 14 million gallons, the Ventura County Environmental Health Division said Thursday. Warning signs have been placed along the river and beaches.
Elsewhere, residents tried to salvage belongings, and rescue crews pulled survivors from beneath collapsed houses Friday in the aftermath of a tornado-spawning storm system that killed at least nine people as it barreled across parts of Georgia and Alabama.
The widespread destruction came into view a day after violent storms flipped mobile homes into the air, sent uprooted trees crashing through buildings, snapped trees and utility poles and derailed a freight train.
Henry Austin is a senior editor for NBC News Digital based in London.
Dennis Romero is a breaking news reporter for NBC News Digital.