By Andy Rose, Holly Yan and Karina Tsui

(CNN) — With parts of Los Angeles County still smoldering from wildfires and new blazes flaring up, expected rainfall this weekend would seem like a welcome relief. But how the rain falls could make the difference between a disaster respite or a disaster repeat.

Los Angeles County faces a high chance of widespread rain this weekend, with light intensities spread across many hours, the National Weather Service said.

There are no major flooding risks, except a 5% to 10% chance of significant debris in burn scars for Los Angeles and Ventura County, the weather service said. Isolated, heavy rain of up to 0.5 inches an hour is also expected.

But the ground in LA hasn’t seen a drop of rain this year. “It behaves more like cement; the ground can’t accept the water, so it all goes to runoff immediately,” said Ariel Cohen, the meteorologist in charge of the National Weather Service office in Los Angeles.

So if the rain falls at a slow, steady pace that can be absorbed by burn-scarred ground, the showers will be helpful.

But brief blasts of rain could cause flash flooding that would loosen soil and debris on charred hillsides, sending it tumbling toward decimated neighborhoods.

“It could result in fast-moving flows of mud, rock and fire debris that all conglomerate and spread quickly downhill,” Cohen said.

“It has the potential to be damaging as it does so, taking down other structures. And certainly could be a threat to life and property.”

Get sandbags before the rain, official warns

Local and state authorities – stung by criticism they didn’t do enough to prevent the wildfire destruction – say they’re ready for potential consequences from the rainfall.

Los Angeles Mayor Karen Bass issued an emergency order to help keep polluted water and mud from entering city storm drains. The city is expediting debris cleanup and installing concrete barriers in burn areas.

More than 250,000 sandbags have been placed in flood-prone areas, the California Department of Water Resources said. Crews also dug pits into hillsides called “debris dams” to catch sediment that might break loose during rainfall.

Residents in areas at risk of landslides should get “sandbags ahead of time” and know how to shut off all utilities at home, Los Angeles County Fire Department Chief Deputy David Richardson said.

He said sandbags are available at local fire stations.

“Stay away from areas susceptible to flooding. Do not attempt to enter moving water,” Richardson warned. “Do not try to rescue someone who is being swept away. Instead, call 911.”

The rain forecast comes on the tail end of another red-flag warning period that prompted nearly 100,000 power customers to have their electricity shut off as a precaution Thursday.

New wildfires flare up

The catastrophic Palisades and Eaton fires, which have killed 28 people and torched more than 40,000 acres since January 7, have not grown much in size in over a week. But a spate of fresh wildfires has tormented Southern California this week.

Two new blazes erupted Thursday afternoon in San Diego County.

The Border 2 Fire torched over 5,300 acres and prompted an evacuation order Friday. The inferno is 10% contained and spreading through the Otay Mountain Wilderness, near the US-Mexico border.

While the Border 2 Fire area is not densely populated, “There is a threat to critical communication infrastructure,” said the California Department of Forestry and Fire Protection, also known as Cal Fire.

The Gilman Fire, south of La Jolla, also started Thursday and torched 3 acres before it stopped moving forward, Cal Fire said.

Back in Los Angeles County, the Hughes Fire has incinerated more than 10,000 acres since it erupted near Castaic Lake on Wednesday. Several areas are under evacuation orders, and the blaze was 56% contained as of Friday.

Haunting memories of past landslides

Forecasters don’t expect the kind of rainfall that led to some of the region’s most destructive recent land flows. The Santa Barbara County community of Montecito was virtually destroyed after a winter storm immediately followed the Thomas Fire, a blaze that killed 23 people.

And the unique geography of Southern California leaves some areas in constant danger of land instability.

The coastal city of Rancho Palos Verdes suffered sudden movement from a decades-old complex of slow-moving landslides last fall, twisting roads and putting multimillion-dollar homes on the brink of destruction.

The city has invested millions of dollars into “dewatering wells,” sucking more than 112 million gallons of destabilizing water out of the ground in a desperate effort to shore up neighborhoods.

A preview of the worst-case scenario following this weekend’s rainfall could be seen in the Palisades two weeks ago, when an oceanview home that survived the wildfire was literally split in half by a mudslide – apparently triggered by runoff from the water used to fight the fire.

“There are mud and debris flow hazards that are existing even when it’s not raining,” Los Angeles County Public Works director Mark Pestrella said.

A fire victim who lost her home says she never got an evacuation warning

Raya Reynaga’s home perished in the deadly Eaton Fire, and the Altadena resident nearly suffered the same fate.

“I did not get a warning. I did not get anybody knocking on my door,” Reynaga told CNN on Friday. “I was the last person on my street. They had to come get me.”

Adding to the chaos: “The day before, we had power outages,” Reynaga said. “That day, it was completely dark black. No power. It was just a nightmare.”

Reynaga is among many residents from historically significant Altadena who say they never got a warning to evacuate during the Eaton Fire, which killed 17 people in Los Angeles County.

A CNN investigation revealed weaknesses in emergency alert systems not just in Southern California, but nationwide.

Los Angeles County officials are now calling for an independent investigation to review the emergency alert system used during the recent Eaton and Palisades fires.

“This independent assessment will also ensure we are better prepared for future disasters and can act swiftly to protect lives and property,” Los Angeles County Board of Supervisors Chair Kathryn Barger said this week.

Reynaga had one message for officials about the missing evacuation alerts:

“Do better, because lives have been lost,” she said. “This is completely unacceptable.”

Trump’s threat to withhold aid would ‘devastate and victimize us all over again’

President Donald Trump is expected to travel to California on Friday after visiting western North Carolina, which was devastated by Hurricane Helene.

California Gov. Gavin Newsom said the White House didn’t tell him about Trump’s visit, but said he’s “glad” the president accepted his invitation.

Trump has threatened to withhold aid to California, saying state officials need to change how they manage water. On Friday, Trump issued another demand before California could get “a lot of help from the US.”

“I want two things: I want voter ID for the people of California … and I want the water to be released,” Trump said during his stop in North Carolina.

In a Truth Social post, Trump falsely implied Los Angeles lacked the water to put out the fires because the governor chose to protect an “essentially worthless fish called a smelt,” which is only found in Northern California.

Reynaga, who said she hasn’t received any financial aid from her insurance company or the federal government after losing her home, called Trump’s threat “terrible.”

“We need to rebuild. We need funding. We need financing,” Reynaga said. “So that would just devastate and victimize us all over again.”

California Attorney General Rob Bonta told NewsNation that putting conditions on aid to a state suffering from a natural disaster is a “great mistake.”

“The president ran for president to be the president of the United States of America, not just the red states of America,” he said. “Doesn’t matter what party preference the state has.”

CNN’s Brandon Miller, Ella Nilsen, Lauren Mascarenhas, Samantha Waldenberg, Jeff Zeleny, Mike Madrigal and Kia contributed to this report.

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