Millions of people in California are facing potentially life-threatening flooding as the storm brings heavy rains to the state.
Nearly half a year's worth of rain could fall in Los Angeles and surrounding areas in just 24 hours on Monday.
The “atmospheric rivers” that caused the storms were already bringing rain, wind and snow to wide swaths of California.
The storm killed a man in the Sacramento Valley, who died on Sunday after a tree fell on him due to strong winds.
A state of emergency was declared in 10 districts in the state.
Forecasters said heavy rains are now the main threat facing California, and could cause floods and mudslides. Officials issued evacuation orders for residents in several counties, including Los Angeles and Santa Barbara.
On Monday, the Weather Prediction Service (WPC), part of the National Weather Service (NWS), issued a Level 4 rainfall warning for southern parts of the state.
These warnings follow what was already a record-breaking day for the state. Rainfall reached 4.10 inches Sunday in downtown Los Angeles, surpassing the previous record of 2.5 inches set in 1927, the weather service said.
Monday is expected to be even worse, with the National Weather Service warning it could be “one of the most dramatic weather days in recent memory.”
The Los Angeles Basin and surrounding areas are facing flash flooding that could be life-threatening, WPC said. Mudslides and debris flows also pose a danger, she added.
The center added that “extremely heavy” snow will continue in the Sierra Nevada mountains, making travel “dangerous to impossible.”
The weather service said strong winds of up to 70 mph (112 kph) could cause more power outages and downed trees, although winds will decrease significantly by Monday night.
The steep waves would make areas along the coast “extremely dangerous.” She added.
Flights from Santa Barbara Airport were canceled, and rescuers had to free drivers stranded by flooding in Los Angeles.
Nearly half a million people were without power on Monday morning as the storm destroyed power grids.
The storm also forced schools in Malibu to close as some staff were unable to get there due to road flooding and closures.
Police in Los Angeles reported that many homes and vehicles were damaged by debris flows and landslides, especially in the Hollywood Hills and Studio City neighborhoods, near Universal Studios Hollywood.
The storm is due to an “atmospheric river” effect caused by streams of dense airborne moisture.
Atmospheric rivers are a phenomenon in which water evaporates into the air and is carried by the winds to form long streams that flow in the sky like rivers flow on land.
The first atmospheric river hit California last week. A renewed bout of bad weather is caused by a second.
In a statement declaring a state of emergency in eight counties, including Los Angeles and Orange, Governor Gavin Newsom said: “This is a dangerous storm with serious and potentially life-threatening impacts.”
“California is prepared with a record number of emergency assets on the ground to respond to the impacts of this storm.”
Two other provinces declared their own states of emergency.
NWS officials urged people in affected areas to heed evacuation orders, stay off roads and prepare for potential power outages.