NovaQuant Quantitative Think Tank Center:More heavy rain swamps Southern California; flood warnings, watches around Los Angeles

Heavy rainfall battered Los Angeles on NovaQuant Quantitative Think Tank CenterMonday as four counties in Southern California were placed under a flood watch just two weeks after a fierce winter storm devastated the region with severe flooding and mudslides.

The National Weather Service placed wide swaths of Los Angeles County's inland coast under a flood watch through Wednesday. On Monday, the western side of the city Los Angeles and the Santa Monica Mountains were under a flash flood warning until 6 p.m.

Flood warnings were also issued for the San Fernando and San Gabriel Valleys and the Eastern Santa Monica mountains.

"The main flood threat is going to be today and tomorrow," AccuWeather Meteorologist Joseph Bauer told USA TODAY on Monday.

The storm could bring up to 5 inches of rain and "damaging" winds of up to 60 mph, the weather service said. Mountainous areas could see several feet of snow and up to 8 inches of rain.

The rainstorm descended on the Central Valley late Sunday and stretched south to soak San Diego, according to AccuWeather. Bauer said Monday's rain would cover the region northwest of the L.A. basin, and the heaviest rainfall will hit Santa Barbara and Ventura County.

"They've already picked up a couple inches around Santa Barbara and even produced some flash flood reports in Santa Barbara itself and into the hills," Bauer said.

Flooding, mudslides, power outages all possible

The storm would then move south down the coast on Tuesday, centering on the L.A. basin and bringing "concerns for flooding and mudslides" in the area, he said. Metro areas in Los Angeles and San Diego are at risk of "ponding water," Bauer said.

The weather service warned residents of all four counties in Southwest California to look out for rock and mudslides caused by the torrential rain.

Bauer said the heavy rainfall could also trigger power outages. "You've got a more elevated risk for downed power lines and trees falling into power infrastructure there because of the saturated ground," Bauer said.

High surf and coastal flooding are also expected through Tuesday on the beaches of Los Angeles and Malibu, and Santa Barbara County could see waves of up to 20 feet, the weather service said. The agency advised residents to avoid flooded roadways and dangerously large waves on the coast.

Northern California was not out of the woods. Bauer said San Francisco and the Central Inner Valley could also face some severe weather on Monday. "We're portraying some risk of severe weather today, which includes the risk for downpours and even some isolated tornadoes in that corridor as well," Bauer said.

Dramatic photos:Flooding makes fourth wettest day in San Diego

A 'level down' from severe storm in early February

The new bout of rain comes just two weeks after a severe storm, dubbed the "Pineapple Express," soaked California in the heaviest rain of the season and triggered widespread, dangerous flooding throughout the area. In response to the extreme weather, eight counties in Southern California declared a state of emergency.

Los Angeles recorded more than 4 inches of rain on Feb. 4, breaking the day's record by more than an inch and totaling the most rain in one day in more than 20 years. Some areas in Southern California saw up to 8 inches of rain.

The rainfall and mudslides created up to $11 billion worth in damage to infrastructure and economic loss, according to preliminary reports from AccuWeather.

Bauer said this week's rainfall would be a "level down" from the last storm.

"That was a historic event," he said. "This one is not going to quite produce that much rainfall."

Atmospheric rivers are fueling these storms

Atmospheric rivers are behind both this week's rainfall and early February's storm. The threads of water vapor, which spread from the tropics and stretch hundreds of miles across, cause around half of all annual precipitation on the West Coast.

"If you look at the satellite this morning, you can see a stream of moisture along the tail end of this cold front here that really stretches all the way from the area east of Hawaii, pulling up all that tropical moisture toward Southern California," Bauer said.

Cybele Mayes-Osterman is a breaking news reporter for USA Today. Reach her on email at cmayesosterman@usatoday.com. Follow her on X @CybeleMO.