Highlighting a remarkable beginning to the winter rainy season, the National Weather Service on Friday issued a flash flood watch for parts of the greater Bay Area as a powerful storm continued to churn toward Northern California, bringing heavy rains and gusty winds to the region on Saturday night and Sunday.
The category 5 atmospheric river storm — the highest on a scale of 1 to 5 — is forecast to deliver on Sunday the most rain to the Bay Area of any single day in more than two years.
“The Bay Area is ground zero,” said Marty Ralph, director of the Center for Western Weather and Water Extremes at UC San Diego. “We are still on track for a major storm.”
The storm, which will arrive Saturday night from the Pacific Ocean and continue until Monday morning, could bring up to 9 inches of rain in the North Bay, 5 inches in the Santa Cruz Mountains and 1 to 3 inches in Bay Area cities, the National Weather Service said.
The last time San Francisco received more than 2 inches of rain in 24 hours was 32 months ago — on Feb. 13, 2019. The last time a storm this big hit the Bay Area in late October was 11 years ago, Ralph’s research found.
“We’re going to have slick roads, some flooded intersections, power outages,” said Jan Null, a meteorologist with Golden Gate Weather Services in Half Moon Bay. “This is a real winter storm. It has significant wind and significant rain.”
(1/5) Last AR update before this weekend’s #AtmosphericRiver. The GFS continues to forecast IVT magnitudes >1200 kg/(ms) over the Bay Area on Sunday. pic.twitter.com/6lxPhgQVsO
— CW3E Scripps (@CW3E_Scripps) October 22, 2021
With 35 mph winds expected Sunday and gusts up to 60 mph in some areas, falling trees and power lines are a concern. PG&E warned that widespread power outages were possible.
The utility has put 350 crews on standby from across the state, said PG&E spokeswoman Deanna Contreras, with triple the normal number in some areas.
“It’s pretty much all hands on deck. Anyone who will be available for this weekend will be working,” she said.
Because of California’s ongoing two-year drought, emergency officials don’t expect rivers to flood. But there were growing concerns about mudslides where fires burned in the Santa Cruz Mountains, Sonoma and Napa counties, Big Sur and the Diablo Range east of Milpitas to Gilroy. The National Weather Service’s flash flood watch includes those areas.
“This is an exceptionally wet and strong system,” said Ryan Walbrun, a meteorologist with the National Weather Service. “Out of an abundance of caution, we wanted to draw attention to the burn scars.”
Officials in Santa Cruz County said they were considering potential evacuations for up to 200 homes in the most high-risk areas where the CZU Lightning Complex Fire in August 2020 destroyed 1,400 structures and burned nearly 90,000 acres between Boulder Creek and Big Basin Redwoods State Park.
“We are concerned with the weather,” said Nicole Coburn, assistant county administrative officer for Santa Cruz County. “We are trying to figure out if there might be a need for narrow evacuations.”
Periods of heavy rainfall are possible late Saturday into Tuesday, with 2-5″ in the Valley and 3-10″ in the foothills and mountains. This could bring the potential for roadway and small stream flooding as well as ash & debris flows on recent burn scars. #CAwx pic.twitter.com/KwYYpWFOpc
— NWS Sacramento (@NWSSacramento) October 22, 2021
Mark Bingham, chief of the Boulder Creek Fire Protection District, said county officials and private contractors have been working to rebuild culverts, re-seed hillsides, remove dead trees and take other precautions in the burned areas over the past year.
“We’ve been planning for this all summer,” Bingham said of his department. “Maps have been updated, people have been briefed. Training has been going on. Supplies have been restocked. We’re watching it carefully, and we’re ready to respond.”
In counties around the Bay Area, public works crews were being beefed up for the weekend.
“We’re making sure that our storm water conveyance systems are clean and clear and there’s no obstruction, our storm water pump stations are functioning properly and making sure any litter in our drain system is removed,” said John Medlock, deputy public works director in Alameda County. “We have crews on standby 24-7.”
Walbrun said Saturday morning and afternoon will be dry. Residents may want to clear gutters, bring in garbage cans and wind down patio umbrellas, he said. Lawn sprinklers should be turned off. Charging cell phones and having batteries for radios in the event of power outages also is recommended, he added.
“If you don’t have to travel on Sunday, maybe don’t,” he added.
The Sierra Nevada region was expected to receive 2 to 3 feet of new snow. The National Weather Service issued a winter weather watch from Mount Shasta through Lake Tahoe and down to the Southern Sierra, warning of chain controls and closed roads in the mountains.
The powerful storm follows a week of rain across Northern California. But much more will be needed to bring up reservoir levels around the state after the driest two years in a row since 1976-77, water managers said.
“It is not nearly enough to end the drought,” said Tony Estremera, chairman of the Santa Clara Valley Water District. “We must continue to conserve water whenever possible.”
The rain has all but ended fire risk this year in some areas. From Monday through Friday afternoon, Mount Tamalpais in Marin County received a stunning 10.3 inches of rain. Mount Diablo in Contra Costa County had 4.51 inches, and Ben Lomond in the Santa Cruz Mountains received 3.1 inches.
In urban areas, San Francisco received 1.81 inches since Monday, double its historic average for the month of October. Oakland had 1.19 inches, and San Jose, which was limited by the “rain shadow” effect of the Santa Cruz Mountains, had .28 inches.
If this storm brings another 2 inches to San Francisco, as predicted, it would rank this month among the five wettest since 1849 when modern weather records there began, Null said.
“The storm door is open,” he said. “We still need a lot more rain. But we’re off to a good start. And that’s better than being off to a bad start.”
Source: www.mercurynews.com