A person walk along a pier as an atmospheric river of rain continues to impact the weather in Oceanside, California [Source: Reuters]

A deadly atmospheric river storm lingered over Southern California for a third day on Tuesday, soaking the region with steady rains that threatened to trigger more flooding and mudslides as the weather system slowly crept toward the Desert Southwest.

After a day of record-breaking rainfall across the Los Angeles area, a flood watch remained in effect for much of Southern California through Tuesday afternoon. A flash-flood warning was posted for the Orange County coast, and flood advisories were issued as far south as San Diego and the U.S.-Mexico border.

As rain continued to fall throughout Los Angeles, work crews and residents were cleaning up after the storm felled more than 250 trees and triggered 380-plus mudslides across the nation’s second-largest city as of Monday night, authorities said.

Downed trees and utility lines knocked out electricity to hundreds of thousands of homes and businesses, including 156,000 utility customers who remained without power in Los Angeles alone as of Tuesday.

L.A. Fire Chief Kristin Crowley said at least three dozen buildings required inspection due to mudslide damage and hillside slope failures. Seven have been red-tagged as unsafe for occupancy.

Barry Blocker, 55, a retired police officer, said he spent several hours on Monday digging his car out from a cascade of mud that had poured down a hillside onto his driveway before dawn. The house where he has lived in L.A.’s Baldwin Hills district for 23 years without incident was undamaged.

Prolonged downpours that dumped 6-12 inches (15-30 cm) of water have left the ground so “super-saturated” that it will take very little additional rain to trigger further landslides and debris flow, said Ariel Cohen, chief forecaster for the National Weather Service (NWS) office in Los Angeles.

The intense rainfall, with heavy snows in the mountains, was carried to California by a storm system meteorologists call an atmospheric river, a vast airborne current of dense moisture funneled inland from the Pacific.

The latest tempest, and a less powerful storm that hit California last week, also qualified as a “Pineapple Express,” a type of atmospheric river originating from subtropical waters around Hawaii.

While such storms are not uncommon to the West Coast, meteorologists say they are likely to become more frequent and extreme over the next century if planetary warming from human-induced climate change continues at current rates.

Scientists say the prevailing El Nino weather pattern also may be contributing to some of the recent storm activity along the Pacific coast.

The latest storm kicked off in California with powerful winds gusting to 75 miles per hour (121 kph) and higher across northern and central California on Saturday, before spreading into South California early on Sunday.

At least three people were killed when wind toppled trees on Sunday in Sacramento, Santa Cruz and Sutter counties, authorities said.

While diminishing rain and thundershowers were expected to loll over the greater Los Angeles and San Diego areas Tuesday, increasing precipitation was forecast for the California desert and Colorado River Basin as the storm front drifts into Arizona.

In Los Angeles, the onslaught will linger in the record books as one of the wettest storms in more than 150 years, meteorologists say, as well as in the minds of those who experienced it.