An Atmospheric River Has Arrived In SoCal, Bringing Heavy Rain, Flooding And Rockslides

Southern California's wet, rainy week is getting more intense Thursday, thanks to an atmospheric river that's made its way into the region.

Up to 4 inches of rain could fall in the foothills and mountains, while 1 to 3 inches is forecast for the coasts and valleys, according to the National Weather Service.

Storm systems like the one we're seeing (and hearing) today begin far out at sea and gather abundant moisture as they travel towards land, often driven by high winds. Atmospheric rivers can hold more than 10 times the amount of water found in the Mississippi River. All that rain can be a boon for the region, but also carries threats.

Heavy rain from an atmospheric river last January pounded Santa Barbara County, leading to the deadly Montecito mudslides. And Thursday's storm is sparking similar concerns.

DEBRIS FLOW IN HOLLYWOOD HILLS

A "precautionary local evacuation" was underway in a Hollywood Hills neighborhood as of 10:30 a.m. after a reported mud and debris flow from a home that was under construction, according to L.A. city firefighters.

No injuries have been reported, but LAFD officials said homes above and below the site in the 1800 block of Stanley Avenue, as well as some on Nichols Canyon Road north of Courtney Avenue, are being cleared. Department of Building and Safety officials are on the scene.

Authorities have "minimal concern" that the home being built would slide down the hillside, given how securely it's been anchored in the bedrock, according to LAFD spokesman Brian Humphrey.

HILLSIDE COLLAPSE IN ECHO PARK

A car was totaled and a house was red tagged after the collapse of a hillside in Echo Park.

FLOODING

Flash Flood Warnings and watches issued earlier in Santa Barbara, Ventura and Los Angeles counties were canceled just before 9:45 a.m., according to NWS forecasters.

"Some areas may remain dangerous from earlier rains," forecasters said. "If you evacuated, wait for instructions from emergency officials before returning."

A flood warning does remain in effect for the Ventura River at Foster Park. The river rose 10 feet in three hours with "high flows in the river and minor flooding expected near the Ventura Beach RV Park" near the 101 Freeway, according to officials.

Ventura police said they were relocating campers at the RV park to the Ventura State Beach parking lot. Police also said W. Main Street was closed at Peking Street "until further notice." Images and video shared by NWS showed the a section of the park flooded, with a few vehicles half submerged.

Twelve people were evacuated after becoming stranded in the Santa Ana River in Jurupa Valley.

ROAD CLOSURES AND ROCKSLIDES

Elsewhere, the rain (and bad driving in that rain) caused traffic havoc, with some roads closed due to crashes or rockslides. That includes Topanga Canyon Boulevard, which has been shut down between Pacific Coast Highway and GrandView Drive after rocks, mud and debris fell onto the roadway.

In Malibu, a woman hiking in the Santa Monica Mountains was critically injured after being "pummeled" by a falling boulder above Rambla Pacifico Street, according to officials from the Lost Hills Sheriff Station. The 57-year-old hiker was taken to a hospital in critical condition.

EVACUATIONS

The evacuation orders for the Woolsey Fire burn area have been lifted.

Still, fire officials warned residents to be cautious when returning to the area, as there are still patches of road partially covered by rock and mud, running streams of water and the danger of falling rocks and further debris and mud flows. Avoid any flooded areas and road crossings.
In Riverside County, new mandatory evacuations were ordered for some residents in the Holy Fire burn area. The full list can be found here. An evacuation center has been set up at Temescal Canyon High School in Lake Elsinore, 28755 El Toro Road.

Evacuation orders remain in effect for the following areas in Ventura County:

• Ventura RV Beach Resort
• The South Coast area to Malibu
• Matilija
• Wheeler Springs
• North fork (extending along Oso Road)

HOW MUCH RAIN ARE WE GETTING?

NWS officials said this week's storms have dumped nearly a foot of rain in the region.

As of this morning, the greater L.A. area has now received about 56 percent of the rain we typically see in a rain year, which ends in September. That puts us comfortably ahead of our usual pace.

ADDITIONAL INFORMATION AND RESOURCES

For updates throughout Thursday, including lists of road closures, evacuation orders, and flood warnings, check the following sites:

• Los Angeles County
  
• Ventura County
  
• Santa Barbara County
• National Weather Service Los Angeles
• California Highway Patrol on Twitter
  
• Caltrans District 7 on Twitter
  
• City of Malibu
  
• L.A. County Fire Department on Twitter

This is a developing story. Check back for updates.

Science reporter Jacob Margolis and data reporter Aaron Mendelson contributed to this story.

UPDATES:

5:39 p.m.: This article was updated with information about a hillside collapse in Echo Park and a river evacuation in the Jurupa Valley.

4:17 p.m.: This article was updated to indicate that evacuation orders were lifted for the Woolsey Fire burn area.

1:27 p.m.: This article was updated with information from L.A. County sheriff's officials.

11:38 a.m.: This article was updated with information from NWS.

10:48 a.m.: This article was updated with information about a mudslide from LAFD.

10:34 a.m.: This article was updated with new information from NWS.

9:28 a.m.: This article was updated with data from our newsroom's rainfall tracker.

9:05 a.m.: This article was updated with information from Caltrans.

8:48 a.m.: This article was updated with information from the National Weather Service and Ventura police.

This article was originally published at 7:10 a.m.