What to Know
A storm fueled by an atmospheric river pulling Tropical moisture into California is expected to arrive Wednesday
Widespread rainfall is expected by Thursday morning, marking the final round of rain during a week of storms
Several hillside areas were under evacuation orders ahead of the storm
Southern California faces a third consecutive day of rain as another Pacific storm fueled by a conveyor belt of moisture bears down on the West Coast.
This round is expected to bring widespread rainfall and the threat of mudslides as more moisture is added to already soaked hillsides in the region's wildfire burn areas. Residents in parts of Malibu, Burbank, and Ventura and Santa Barbara counties were under evacuation orders.
A week of storms left those communities and others around the state concerned about the potential danger for thousands of people living in foothill and canyon areas devastated by last year's wildfires. Immense areas of the state were razed by wind-whipped flames, leaving hillsides bare of vegetation that could stabilize soil and prevent mudslides.
The heaviest rains will move in late Wednesday and early Thursday due to a phenomenon called an atmospheric river. The robust plume of subtropical moisture ushers tropical air up from the Pacific like a conveyor belt. The long, narrow band of water vapor in the sky makes land, then glides up from sea level and condenses, turning to rain. In a typical year atmospheric rivers account for about 30 to 50 percent of the West Coast’s annual rainfall. They've contributed to historic rain seasons and flooding, including the 2017 winter storms and the Great Flood of 1862, which devastated parts of the state.
"We'll be watching later tonight when that rain really picks up," said NBC4 forecaster Shanna Mendiola. "This (storm) is not going to be as cold. We're going to be tapping into the atmospheric river of moisture."
Several thousand people heeded a mandatory evacuation order in Santa Barbara County on the Central Coast, where last year a sudden debris flow swept through Montecito, killing 23 people and destroying 100 homes.
Daphne Moore was among the evacuees.
"It's a complete drag but it's better than dying in a mud debris flow," Moore said.
Some mandatory evacuations remained in the Malibu area of Los Angeles County and voluntary evacuations were in place for some parts of Ventura County. Both were affected by November's Woolsey Fire that destroyed more than 1,500 homes and killed four people.
In Northern California, an evacuation warning is in place for Pulga, a neighboring town of Paradise, which was incinerated two months ago by the Camp Fire that killed 86 people.
A blizzard warning for much of the Sierra Nevada Mountains and Lake Tahoe takes effect Wednesday night. The snowfall is a good sign for California's snowpack, which melts in the spring and runs off into the state's aqueduct system.
The north could see the strongest storm of the year with heavy rain in the San Francisco Bay Area leading to a widespread flash flood watch beginning in the afternoon. Flood and high wind watches were scheduled for the Sacramento area, with the weather service warning that gusts could lead to power outages, downed trees and tough driving conditions.