Driven by an atmospheric river known as “the Pineapple Express,” which moves heavy moisture from the tropical climes of Hawaii to rain on the West Coast, the storm is expected to deliver months’ worth of rain in the next few days.

“Severe, widespread flash flooding is expected,” the National Weather Service said, adding that “lives and property are in great danger.”

The first burst of heavy rain hit the region overnight Tuesday, with more expected Wednesday.

Storm impacts were already being felt across California on Wednesday morning with trees and power lines being knocked down all around the state.

Authorities in Los Angeles County warned there was potential for “debris flows” in areas devastated by wildfires in January. They urged residents to monitor weather updates and avoid unnecessary travel.

National Weather Service meteorologist Ariel Cohen told reporters in Los Angeles that from late Wednesday through Friday, “many areas will likely be experiencing significant flooding, along with rockslides and mudslides, especially through the high terrain and canyon roadways.”

Some southern California communities could see up to 12 inches (30.5 centimeters) of rainfall, Cohen said on Tuesday.

Some Californian communities are still reeling from thousands of wildfires that killed 31 people across the state during 2025, including residential neighborhoods of Los Angeles such as the Pacific Palisades.

Flood watches were in effect for much of Los Angeles County and other parts of the state.

More than 200 homes were placed under evacuation orders Tuesday, according to LA law enforcement.

In the Sierra Nevada, the major mountain range along the eastern border of California, more than a foot of snow had already fallen this week, with up to five feet of snow forecast before the storm is through.

The storm was also expected to bring wind gusts of up to 55 mph (88 kph) across the state.

“The combination of increasingly saturated soil and the strong winds will bring the potential for widespread downed trees and power lines,” weather officials warned. “Lives and property are in great danger.”