California is still reeling from last week's severe weather, which brought widespread damage in the state's northern region. [Source: BBC News]

California is bracing for more severe weather this week, with forecasters warning of an incoming “relentless parade of cyclones”.

The US state has already suffered a week of torrential downpours and damaging winds that killed 12 people in 10 days, Governor Gavin Newsom said.

More than 120,000 people are still without power as of Monday morning.

The governor warned on Sunday that the most brutal weather is due in the next 48 hours.

“We expect to see the worst of it still ahead of us,” Governor Newsom said at a news conference. “Don’t test fate.”

This new round of severe weather will bring heavy rain on already flooded rivers, damaging winds that are expected to topple trees and power lines, and heavy snow in northeast California.

The US National Weather Service (NWS) said the heaviest and most widespread rain will likely occur around Tuesday morning and afternoon, and have issued a flood warning in areas around Los Angeles, including Orange County and the San Bernardino County Mountains.

The Sacramento Valley is also under a flood advisory. Schools in and around Sacramento have cancelled classes on Monday in anticipation of the storm and amidst widespread power outages.

US president Joe Biden declared a state of emergency for California on Monday, which allows the Federal Emergency Management Agency, also known as FEMA, to provide disaster relief.

Atmospheric rivers can cause extreme rainfall and floods. Bomb cyclones require a mix of high and low temperatures, rising and dropping air pressure, and moisture, often resulting in strong winds and severe storms.

Last week’s storms inflicted widespread damage in northern California and dumped record-breaking rain.

The storm damaged homes and businesses, and killed at least 12 people. Among the victims was a toddler who died after a redwood tree fell onto a mobile home in northern California.

A woman who lived in a homeless encampment along the Sacramento River also died on Saturday when a tree branch fell on her tent.

Much of the area hit by heavy rainfall has been under extreme drought conditions. Last year, California issued caps on how much water residents can use in an effort to conserve its depleting supply.

Despite the rain, much of the state remains under moderate to extreme drought warnings, according to the US Drought Monitor.

Experts have said that it would take many years of rain to reverse the two-decade-long drought that has hit the western US.