The storm expected to follow Sunday's scattered showers will bring risks of significant flooding and debris flows across Southern California, forecasters warned.
While less than a tenth of an inch of precipitation was predicted for Sunday, the system moving into the region on Tuesday and Wednesday could bring 1 to 3 inches of rain along with gusty winds.
Snow levels are expected to drop to 6,000 to 7,000 feet.
"Slippery roads and traffic delays should be expected during heavier showers," the National Weather Service said.
The agency said mudslides and rockslides could also occur on and below canyon roads.
There's a possibility that the showers linger into Thursday and Friday, and that another storm arrives the following Sunday and Monday, according to the Weather Service.