With an “atmospheric river” set to hit the Bay Area starting Sunday, the National Weather Service on Friday issued a Flash Flood Watch for parts of the region, particularly areas that burned in wildfires last year.
The flood watch will be in effect from 5 a.m. to 11 p.m. Sunday in the North Bay, 1-11 p.m. in the Santa Cruz Mountains, and 5 p.m. Sunday to 4 a.m. Monday in Monterey County, according to the weather service.
Heavy rainfall — forecasters are predicting several inches of rain Sunday and Monday in some areas — could lead to debris flows and flash floods, particularly in areas that burned in fires sparked by lightning storms in August 2020.
Jonathan Cox, deputy chief of Cal Fire’s San Mateo Division, said Friday that rainy weather coming through the region this past week has helped quell immediate concerns over any new major wildfires starting and “is very welcome for a lot of reasons.”
However, the burn scars from the CZU Lightning Complex fires in San Mateo and Santa Cruz counties last year are among the areas under the flood watch as the larger storm descends on the region this weekend.
“It’s good news for the fact that it will reduce the wildfire risk, but any change in the weather will have another set of risks,” Cox said.
Cal Fire and other first responder agencies in the two counties are encouraging people to check Zonehaven, a platform that helps communicate real-time evacuation information to the public and divides areas into evacuation zones. People can look up their address to find out their zone at community.zonehaven.com.
Along with knowing their evacuation zone, Cox recommended that people in both San Mateo and Santa Cruz counties sign up for their respective county’s emergency alert systems to receive text or voice messages in the event of an emergency.
In San Mateo County, the Office of Emergency Services is encouraging residents to prepare their homes for the coming wet weather.
“Now is the time to check roof drains and down spouts to make sure they are clear of debris,” Dan Belville, head of the County’s Department of Emergency Management said in a press release. “And make sure you have flashlights with fresh batteries and other essentials handy. The time to discover you need emergency supplies is before you need them.”
Public Works crews will be patrolling locations prone to flooding and roads affected by last year’s CZU Lightning Complex fires, including Gazos Creek Road, Canyon Road, Wurr Road and Cloverdale Road.
The National Weather Service for the San Francisco Bay Area issued a high surf advisory through Friday for a portion of the coast and a flash flood watch Sunday for parts of the region, especially in areas burned by last year’s wildfires. Strong winds are also expected Sunday, with gusts of up to 60 mph at the windiest spots.
The weather service said elevations above 9,000 feet in the Sierra Nevada could get 18 inches of snow or more from Sunday until Monday morning and warned of possible power outages and road closures.
Mike Pierre, owner of Mission Ace Hardware and Lumber in Santa Rosa in Sonoma County, said they sold out of tarps this week and expect to do so again in advance of Sunday’s big storm.
But there is a feeling of relief that the area could escape wildfire this year, unlike last year when the Glass Fire broke out in late September and destroyed nearly 1,600 homes and other buildings. Customers had been stocking up on generators and power cords to prepare, Pierre said.
“People were bracing for that, and it never happened,” he said, “and hopefully, this rain will keep it from happening.”
But burn areas remain a concern, as land devoid of vegetation can’t soak up heavy rainfall as quickly, increasing the likelihood of mud or debris slides and flash flooding that could trap people.
Paul Lowenthal, an assistant fire marshal with the Santa Rosa Fire Department, said the city is providing free sand and bags for residents who need to control rain run-off. They are also asking residents to clear gutters and on-site storm drains as the city prepares for up to 6 inches of rain.
“Given the volume of water we’re expecting, we want it to go where it needs to go,” he said.
Californians rejoiced when rain started falling this week for the first time in any measurable way since spring. NWS Bay Area tweeted that San Francisco International Airport set a record rainfall for Thursday, with 0.44 inches of rain tallied. The old record was 0.13 inches on the same day in 1970.
Rain and snow will continue soaking central and Northern California before spreading into Southern California on Monday.
The storms have helped contain some of the nation’s largest wildfires this year, including one that threatened the popular Lake Tahoe resort region this summer. That wildfire is now 100% contained after snow blanketed the western side of the blaze and rain dropped on the eastern side.
But this week’s storms won’t end drought that’s plaguing California and the western United States. California’s climate is hotter and drier now and that means the rain and snow that does fall is likely to evaporate or absorb into the soil.
California’s 2021 water year, which ended Sept. 30, was the second driest on record and last year’s was the fifth driest on record. Some of the state’s most important reservoirs are at record low levels. Things are so bad in Lake Mendocino that state officials say it could be dry by next summer.