Powerful storm hits California amid warnings of ‘potentially historic rain’

A powerful storm has roared ashore in California, flooding highways, toppling trees and causing mud flows in areas burned bare by recent fires.

After months of drought, the darkened clouds collecting over the state this weekend were a welcome sight to some. But rather than the much-needed drizzle residents and officials hoped could end a disastrous fire season and dampen dried landscapes, the state got a deluge. Some areas are forecast to see more than 10in (25cm) of rain and thousands across the state have lost power.

“A powerful west coast storm is likely to produce areas of heavy rain with life-threatening flash flooding, especially on burn scars, high winds, and significant waves along the coast,” the National Weather Service reported Sunday, adding that “some areas that normally do not experience flash flooding will flood”.

Drenching rain and strong winds accompanied the arrival of an “atmospheric river” – a long and wide plume of moisture pulled in from the Pacific Ocean that was predicted to move south over the next few days. The weather service’s Sacramento office warned of “potentially historic rain”.

Forecasters predict the record-breaking rainfall and strong winds will continue into Tuesday, wreaking havoc across the northern part of the state, especially in areas close to where fires burned over the last two years.

“If you are in the vicinity of a recent burn scar and haven’t already, prepare now for likely debris flows,” the weather service wrote on Twitter. “If you are told to evacuate by local officials, or you feel threatened, do not hesitate to do so. If it is too late to evacuate, get to higher ground.”

Evacuation orders were issued in several areas – from parts of San Mateo county that burned in 2020 to Santa Barbara county where the Alisal Fire that still hadn’t been fully contained by Sunday morning – and the California Office of Emergency Services also deployed crews to assist in burn scars through the Sierra Nevada range.

“This is a reminder to have your go-bag ready and heed any warnings from officials,” the agency tweeted, noting that state emergency resources were being sent to help counties navigate the storm. “Like during a wildfire, if told to evacuate, don’t wait!”

The Bay Area is also bracing for record rainfall that is forecast to continue through the day. Debris flows and floods were reported in the North Bay, in parts of Marin, while roads were closed in San Francisco, Berkeley and Oakland. By sunrise on Sunday, Mount Tamalpais just north of San Francisco had recorded over 6in of rainfall during the previous 12 hours, according to the National Weather Service.

The storm is also producing hurricane-force winds that are tearing across the Bay Area, toppling trees. Gusts higher than 50mph have heightened the risks as roads were blocked and homes had to be evacuated.

“Peak gusts have been around 70mph on higher peaks with 40 to 50mph gusts filtering into lower areas,” the weather service said. “Expect the winds to linger within the main rain band but cut back before the rain begins to let off.”

There are concerns that California’s unhoused residents, most of whom reside outside on the streets and sidewalks, will be in danger from from heavy rains. More than 161,500 people typically experience homelessness in the state on any given day, according to official counts from 2020, organizations have already begun calling for help for those whose shelters were overcome by the storm.

About 150miles (241km) to the north, the California Highway Patrol closed State Route 70 in Butte county because of mudslides within the massive Caldor Fire burn scar.

“We have already had several collisions this morning for vehicles hydroplaning, numerous trees falling, and several roadways that are experiencing flooding,” tweeted the highway patrol’s office in Oroville. “If you can stay home and off the roads today, please do. If you are out on the roads, please use extreme caution.”

Burn areas remain a concern, as land devoid of vegetation can’t soak up heavy rainfall as quickly, increasing the likelihood of mudslides and flash flooding that could trap people.

Recent storms have helped contain some of the nation’s largest wildfires this year. But it remains to be seen if the wet weather will make a dent in the 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 30 September, 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.

Close to 94% of California is currently experiencing severe drought, as categorized by the US Drought Monitor, and scientists with the National Weather Service’s climate prediction center have said that much of the western region is so dry that it would require “sustained above-normal precipitation for several weeks for meaningful improvements”. This torrential rain event will have an impact to the north, but is unlikely to affect the thirsty south-west.

Climate change, which intensified drought conditions with higher heat that baked moisture out of the land and atmosphere, has also set the stage for greater extremes like the storm currently pummeling the west coast.

“A lot of times when we talk about whether it was a wet year or dry year you average the whole season,” John Fasullo, a scientist at the National Center for Atmospheric Research (NCAR) told the Guardian. “But with climate change, you have greater amounts of rainfall being delivered in shorter bursts.” That is much more damaging, especially after fires, he said, adding that climate change has produced a “multiplying effect”.

• The Associated Press contributed reporting