First wave of atmospheric river drenches Southern California

LOS ANGELES – The first wave of a “very dangerous” atmospheric river storm dumped rain on the Southland Wednesday, flooding some roadways, triggering rockslides in some mountain areas and raising fears of debris flows in recent burn areas, where residents were under evacuation warnings or orders.

Fire crews and law enforcement were keeping close watch on the Palisades and Eaton fire areas, in addition to other burn zones throughout the region, as the rain intensified overnight and through the morning.

“Widespread and significant urban flooding will be likely along with rock/mudslides and debris flows (with the threat not just confined to burn areas),” according to the National Weather Service. “Streams, rivers, and creeks will also see rapid flows, thereby increasing the threat of swift water rescues and there is a possibility of some localized river flooding. ”

Forecasters warned anyone traveling on Christmas Eve or Christmas Day to exercise the utmost caution on roadways.

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Flash flood warning

A flash flood warning will be in place until 6 p.m. Wednesday for the bulk of Los Angeles County.

NWS meteorologist Ariel Cohen told KNX News just before 9 a.m. Wednesday that 4 to 8 inches of rain had already fallen in some higher-terrain areas of Ventura and Los Angeles counties, and there were reports of numerous mountain rockslides.

As of noon, nearly 2.7 inches of rain had fallen in Bel Air, more than 4.5 inches in Pacoima, nearly 4 inches in Canoga Park and 2 inches in downtown Los Angeles, according to the NWS. More than 10.6 inches were reported at the San Gabriel Dam and nearly 8 inches at Crystal Lake.

As the rain continued through the morning rush hour, major crashes were reported on multiple freeways. The northbound Golden State (5) Freeway had lanes blocked due to flooding in Sun Valley, where a vehicle wound up inundated in the water. Flooding was also reported on the westbound Ventura (101) Freeway in the Van Nuys area. There were also reports of large rocks falling onto the Antelope Valley (14) Freeway in Agua Dulce.

Power outage

Thousands of residents also lost power by Wednesday morning amid the storm. As of 11 a.m., about 10,700 Los Angeles Department of Water and Power customers were without power. Southern California Edison was also reporting a series of outages across the county, but it was unclear how many people were affected.

The mayor’s office reported at 11 a.m. that about 20 traffic signals around Los Angeles were out, and 43 downed trees had been reported, and the Los Angeles Police Department had responded to more than 50 traffic crashes, while the fire department responded to at least two river-rescue calls.

At a news conference Tuesday, Cohen said lower elevations such as downtown Los Angeles and points south will likely get 2 to 4 inches of rain over the next few days, but areas to the north and west such as the Santa Monica Mountains, San Fernando Valley, San Gabriel Mountains and foothills, Hollywood Hills and northern sections of the L.A. basin could get 4 to 8 inches.

“In fact, some of our computer model projections indicate over a foot of rain falling in total over the mountains by the end of this week,” he said. “Now I want to clarify, all of this rain will not be falling all at once. Rainfall rates may only approach or marginally exceed the debris flow thresholds, so while debris flows on the burn scars will be possible, in general they should be minor to moderate. However, with as much total rain as what we’re expecting, widespread significant flooding will likely occur in urban and poor drainage areas, especially in and around the higher terrain.

Flooding and mudslides

There will almost certainly be numerous rockslides and mudslides along with areas of severe flooding in urban locations and along freeways, which is why being out on the roads will be exceptionally dangerous.”

He added, “If you’re planning to be out on the roads during the Christmas holiday, please reconsider your plans. By the time we get to late Wednesday through Friday, many areas will likely be experiencing significant flooding, along with rockslides and mudslides, especially through the high terrain and canyon roadways.”

A flood watch went into effect at 4 p.m. Tuesday and will remain in effect through Thursday evening for much of Los Angeles County, with mud and debris flows possible across foothill and mountain areas, including recent burn scars.

Forecasters said rainfall rates ranging from 0.6 inches to 1.25 inches per hour in many areas, with some localized downpours reaching up to 1.5 inches on south-facing mountain slopes.

Evacuation warnings and orders

Los Angeles city and county officials issued a series of evacuation warnings and orders in advance of the storm, which is also being described as a “Pineapple Express” event, picking up excessive moisture as it moves across the Pacific Ocean and makes landfall.

The city of Los Angeles issued evacuation warnings that took effect at 11 a.m. Tuesday and will remain in effect through 11 p.m. Thursday for residents of Pacific Palisades and Mandeville Canyon near the Palisades Fire, and south of Runyon Canyon near the Sunset Fire area.

LAPD Chief Jim McDonnell said 126 homes within the city were under evacuation orders, and officers went door-to-door to alert those residents. He said an evacuation center will be available at the Stoner Recreation Center, 1835 Stoner Ave., in West Los Angeles.

Los Angeles County officials, meanwhile, issued evacuation warnings for residents near the Palisades, Eaton, Agua Dulce, Lidia, Franklin, Bridge, Canyon, Owen, Hurst and Kenneth fires. Those warnings will also begin at 11 a.m. Tuesday.

Sheriff’s deputies were also going door-to-door to high-risk residences to notify them of evacuation orders.

Sheriff Robert Luna said that as of Tuesday morning, 124 homes in the sheriff’s unincorporated coverage area were under evacuation orders. County Public Works Director Mark Pestrella said roughly 260 other homes in various incorporated cities — including the city of Los Angeles — were also under evacuation orders and will be visited by local police departments.    Luna urged residents to heed the evacuation orders and warnings, saying those who fail to do are “putting your lives at risk.”

He also urged people who may have elderly or disabled relatives in the warning areas to “make sure you have communicated with them and …coordinated a plan to get them out.”

Residents can check the evacuation status of their neighborhoods at protect.genasys.com.

In Orange County, mandatory evacuation orders took effect at 8 a.m. Wednesday near the Airport Fire burn scar.

The city of Los Angeles’ Emergency Operations Center was activated Monday in anticipation of the storm and to help coordinate response efforts by the Emergency Management Department, police and fire departments and county Public Works officials.

Residents across the county can visit lacounty.gov/emergency to register for county emergency alerts, and to access links for additional local alert systems managed by other municipalities. (CNS)

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