Swathes of the state received 15 or more inches of rain over the past two weeks, according to the National Weather Service.
Forecasters warned that northern and central California were still in the path of a “relentless parade of cyclones”, promising little relief for the region until the middle of the week.
Atmospheric rivers are partly to blame for the torrential rains in California, as are bomb cyclones, but what are they, and what measures are in place?
What’s happening in California?
California has been hit with turbulent weather as thunderstorms, snow, and damaging winds swept into the northern part of the state, and is now heading south.
The National Weather Service said that between December 26 and January 4, downtown San Francisco recorded its wettest 10-day span since 1871, with 10.3 inches of rain.
As an even stronger atmospheric river rolls in, the National Weather Service has predicted that storms will continue through this week, with the possibility of more flash flooding and mudslides in northern and central California.
According to the Sacramento Municipal Utility District, more than 14,543 customers in the state capital were still without electricity as of Monday, down from more than 350,000, when winds of 60 mph (97 kph) toppled trees into power lines.
What are atmospheric rivers?
Atmospheric rivers are storms that resemble rivers in the sky and dump copious amounts of rain. These storms can result in flooding, mudslides, the loss of life, and significant property damage.
They develop when water vapour from the ground evaporates and is carried by the wind, creating lengthy currents that move in the sky like rivers flow on land.
Atmospheric rivers can carry up to 15 times the volume of the Mississippi River, according to the National Oceanic and Atmospheric Administration. They appear as a trail of wispy clouds that can stretch up to hundreds of miles.
What are bomb cyclones?
As well as atmospheric rivers, the overlapping phenomena of bomb cyclones has also been responsible for causing devastation. Bomb cyclones are caused by a hurricane-force low-pressure system.
Bomb cyclones are often associated with atmospheric rivers and typically form in winter when cold and warm air masses collide. They are also known as “explosive cyclogenesis” or a “weather bomb”.
Atmospheric rivers can power up cyclones, into weather bombs.
Is the storm due to climate change?
The latest storms vividly illustrate the consequences of warmer sea and air temperatures caused by climate change, according to meteorologists.
“These storms are supercharged by climate change,” California Natural Resources secretary Wade Crowfoot told a news conference.
What measures are in place?
People living in the impacted areas have been evacuated and all drivers have limited nonessential travel until the peak of the storm has passed.