The National Weather Service declared “flash flooding emergencies” — its most dire flooding alert — in Tulare County, southeast of Fresno in the southern Central Valley, as heavy rain rapidly melted snowpack in the lower Sierra Nevada. Authorities urged residents to seek higher ground and issued emergency evacuations around midday Friday in low-lying parts of Kern County.
The coastline around San Luis Obispo also faced flash flooding from surging rivers. Parts of the central coast have received nearly 10 inches of rainfall over 24 hours.
Authorities warned that the dangerous flooding could continue into the evening in those areas, with heavy rainfall expected to persist through the afternoon. As of early Friday afternoon, about 55,000 Californians had no power, and more than 9,400 were under evacuation orders.
“We are seeing some flooding that is very dangerous starting to develop,” David Lawrence, a National Weather Service meteorologist, said at a midday briefing Friday.
Nancy Ward, director of the California Governor’s Office of Emergency Services, said at the same briefing that authorities have confirmed two deaths as storm-related, though she did not provide details. President Biden on Friday issued a federal emergency declaration for the state, approving a request from Gov. Gavin Newsom (D) and providing government assistance, including granting eligibility for residents and businesses to file damage claims with the Federal Emergency Management Agency.
Reports of massive trees downed by strong winds and roads rendered impassable by flooding, rocks and debris stretched from Santa Cruz to San Luis Obispo. In Soquel, a key road washed out, leaving residents of foothill communities stranded. Videos captured in Kernville, along the Kern River, and Springville, on the Tule River, showed the waterways surging over their banks, swallowing trees and surrounding waterside communities.
The long-parched Golden State has faced several atmospheric rivers over the past three months, dramatically easing — yet not eliminating — a historic drought. After years of efforts to ration water supplies and improve water-use efficiency, the state now faces problems caused by excess precipitation and the challenges of capturing much of it for drier times ahead.
Though rainfall rates were expected to decrease into Friday evening, Weather Service meteorologists said continuing snowmelt could mean that “flooding impacts will worsen before recovery can begin.” Predicted rains could reach 10 inches in 24 hours in hardest-hit locations.
The deluge was raising concern that inflows could overwhelm some reservoirs, including Lake Oroville, the second-largest reservoir in California. It stores water for the dry season but also provides flood protection for communities downstream on the Feather River.
State officials opened the main spillway of the Oroville Dam for the first time since 2019 in anticipation of a massive influx of water to the lake. Since Dec. 1, the lake has risen 180 feet and is now 60 feet below its maximum elevation.
Levi Johnson, deputy operations manager of the U.S. Bureau of Reclamation, said the massive amounts of snowpack in the Sierra Nevada that were piling up Friday would likely cause “significant challenges this year in managing the high inflows” to reservoirs.
In areas where elevation is between 4,000 and 7,000 feet, heavy rain was falling onto a thick snowpack, turning that snow into a spongy sludge that will bring the risk of structural collapses, as well as avalanches. Avalanche warnings have been issued around Lake Tahoe and Mammoth Lakes, Calif., as well as in Idaho.
At elevations above 8,000 feet or so, an additional six or more feet of snow could fall into the weekend, on top of the 16 feet that fell in the past two weeks.
The atmospheric river, ranking a Level 3 on the Center for Western Weather and Water Extremes’ 1-5 atmospheric river scale, should taper off its waterlogged assault on the West late Friday into Saturday, but the active-weather pattern with repeated rounds of heavy precipitation is expected through next week.
Triggering the heavy precipitation is a low-pressure system west of the Columbia River offshore of the Pacific Northwest. The counterclockwise-spinning low is entraining a filament of rich air from the Central Pacific thousands of miles to the southwest. That conveyor belt of moisture is lashing the coast, steered ashore on jet-stream winds ahead of a cold front.
Given that the storm system is milder than recent atmospheric river events, however, the rain-snow line is being forced to higher elevations.
The National Weather Service Weather Prediction Center is calling the rain event in the lowlands and foothills “dangerous and excessive.”
Because atmospheric rivers carry the bulk of their moisture about a mile above the ground, the heaviest precipitation totals are falling in the higher terrain. That’s where the elevated land mass literally pokes into the moisture stream and helps focus it.
Rain can melt a fresh snowpack — a double whammy, as residents have to contend with the moisture both from the rain and what was stored in the snow.
In the higher terrain, a general four to eight feet of snow is likely, with a few places expected to eclipse 110 inches of snow from this event alone.
The Central Sierra Snow Lab in Soda Springs, Calif., off Interstate 80 near Donner Pass, is at 608 inches for the season to date.
A general three to five feet is expected along Interstate 80 above an elevation of 6,500 feet, with one to three feet for areas above 7,500 feet farther south toward Mammoth Lakes. Winter storm warnings blanket the Sierra.
“Travel could be very difficult to impossible,” the Weather Service wrote. “Blowing snow could significantly reduce visibility. Very strong winds could cause extensive tree damage.”
Gusts of up to 75 mph are likely in the highest terrain, with 45 mph winds in the valleys and gusts of 50 to 60 mph on the coast.
Those winds, combined with the rain that’s destabilizing the snowpack, are leading to dangerous conditions.
“A powerful winter storm with gale-force winds, substantial rain on snow, and high-intensity snowfall above the rain/snow line will lead to widespread avalanche activity in the mountains,” wrote the Sierra Avalanche Center in Reno, Nev. “Large avalanches could occur in a variety of areas and elevations.”
Leonard reported from San Diego. Ian Livingston contributed to this report.