It could rain for days in Southern California starting on Saturday night, potentially in record amounts, creating the conditions for what the National Weather Service described as a “very dangerous situation” Sunday into Monday.
The storm system is also expected to bring several feet of snow to the Sierra Nevada, and powerful onshore winds and intense, damaging surf along the California coast.
Here is what to know.
The effects of this system will begin to be felt in California on Saturday evening, and will last through Tuesday.
The heaviest rainfall is likely south of the Bay Area, and excessive rainfall is most likely from Santa Barbara to Los Angeles.
There could be dangerous flash flooding in places. The Weather Service warned that, starting on Sunday, the Los Angeles River “will fill quickly and become a raging river and a very dangerous place to be.”
There is an extremely high chance — over 90 percent — of at least two feet of snow, especially above 6,000 feet in the Sierra Nevada, causing difficult to impossible driving conditions Sunday and Monday.
This atmospheric river will be stronger than the last two.
This storm will connect to an atmospheric river, a stream of moisture in the sky that is typically a couple of hundred miles wide and can be seen on satellite imagery.
It will carry an abundant amount of moisture from the tropics near Hawaii and as it makes landfall, the mountains will wring the moisture out of the air like a sopping wet towel, causing precipitation to fall in record amounts.
The angle and orientation of the mountains can have a big effect on how much precipitation can be created from an atmospheric river, and this latest system will have a southwest to southerly orientation, which will hit the Transverse Ranges from Santa Barbara to Los Angeles at the perfect angle to create a worst-case outcome.
Making matters worse are the higher ocean temperatures just off the coast.
“Anytime you have these rainfall amounts intersecting with terrain and the built environment, you’re going to have trouble,” said Greg Carbin, the branch chief of forecast operations for the National Weather Service.
