There’s mudslide risk in Southern California after weekend rain that helped ease fires

After historic winter firestorms in Southern California, a late weekend bout of rain brought conditions helpful for easing flames – though it also brought some risk of concerning debris flows through recently burned areas.

Los Angeles officially recorded 0.61 inches Sunday, the most in a day there since late March – and 20 times more than the total winter-to-date amount that had been recorded before this storm system. Additional showers and thunderstorms Sunday night brought the total for the city to 0.95 inches for this system.

As rains fell, a flash flood warning was issued late Sunday for portions of the Palisades and Franklin burn scars as well as Malibu and surrounding locations. It was the first flash flood warning of the traditional wet season issued by the National Weather Service office serving Los Angeles. Mudflows prompted the closures of at least some roads, including in Topanga Canyon and on parts of the Pacific Coast Highway.

“Flash flooding and mud and debris flows caused by excessive rainfall are possible in and near the recent burn scars,” the Weather Service in Los Angeles wrote overnight, noting a separate flood watch until Monday morning in areas around where the recent Hughes Fire had burned.

Amid the elevated risk of debris flow, the large blazes still smoldering in the region were doused by at least a couple tenths of an inch, plus several days of high humidity – allowing firefighters to gain increasing control of the situation. The Palisades Fire was 94 % contained, the Hughes Fire 95 % and Eaton Fire 98 % as of Monday morning.

Rainfall tallies overall for areas on the west side of Los Angeles were mainly near and above an inch through early Monday, including 1.19 inches in Santa Monica, 1.92 inches at the University of California at Los Angeles and 1.06 inches in the Malibu Hills.

Reports of some flooding

Amid occasionally heavy rain, several lanes of the Pacific Coast Highway were reported flooded late Sunday night just east of Malibu. Other instances of overnight flooding included roadways in Santa Monica and the 101 Freeway in east Los Angeles.

Flooding has been isolated and largely caused by a handful of slow-moving thunderstorms that also produced small hail.

Among the rain-driven slides that dotted the region, a notable slide hit Topanga Canyon near the Palisades Fire burn area. Another near the Eaton burn scar northwest of Altadena closed portions of the Angeles Crest Highway overnight Sunday.

A flood watch continued for the Hughes burn scar in northern Los Angeles County early Monday.

Showers on Monday are expected to be less widespread and intense than rains throughout Sunday.

Needed rain falls across whole region

Beyond the immediate Los Angeles area, much of Southern California saw periodic rain over the weekend into early in the week as a cold dip in the jet stream moved overhead Sunday.

High relative humidity has also led to low clouds, drizzle and areas of fog – more typically wintry conditions than seen in recent months.

A sampling of regional rainfall totals logged by the Weather Service includes:

- 1.3 inches in Simi Valley

- 1.24 inches in Malibu (at Pepperdine University)

- 0.95 inches at Los Angeles International Airport

- 0.82 inches in Burbank

- 0.62 inches in downtown San Diego

And in the mountain regions of Southern California, snowfall totals reached 4 to 8 inches.

Moderate totals of upward of a foot were reported in the Sierra Nevada through Sunday, with more falling since. These locations were running much below average for seasonal snowfall going into the weekend, with barely any falling in January before this point.