Southern California storm intensifies, raising the risk of flooding and debris flows

Southern Californians have fled their homes for the second time this year, this time due to heavy rain and debris flows, which threaten to cause fresh damage in places already recuperating from last month's disastrous wildfires.

The largest storm to hit California in nearly a year came Thursday, soaking hundreds of miles of the state. The National Weather Service predicts that coastal areas and valleys in Southern California, including the Los Angeles basin, may receive up to 3 inches of rain through Friday, while mountainous areas will receive up to 6 inches.

Meteorologists say the main issue is the intensity rather than the overall amount of rainfall.

“Rainfall rates are the main concern and due to the increased chance of convective cells there is a higher probability of rainfall rates in excess of 1 inch per hour, which would very likely cause substantial debris flows if they occurred over a recent burn area,” forecasters wrote in a 3 a.m. update.

Heavy rain fell in sections of Los Angeles County late in the morning, extending in scope and severity into the evening. The heaviest rain had eased by Thursday evening, but the risk of mudslides remained. Both the Eaton and Palisades fire burn scars had rainfall rates ranging from 0.5 to 1 inch per hour, which can cause debris floods.

According to Caltrans, the Pacific Coast Highway in Malibu and the Pacific Palisades region will remain closed to traffic in both directions between Chautauqua Boulevard and Carbon Beach Terrace until further notice due to the possibility of mudslides and debris flows.

The most serious fear was that a sudden downpour may produce landslides in wildfire regions. On Thursday, muddy water cascaded across portions of the Pacific Coast Highway, leading officials to block it.

The Weather Service received many reports of high winds in Southern California, with gusts exceeding 77 miles per hour in several spots. In Ventura County, northwest of Los Angeles, awnings and carports were damaged by wind.

Elsewhere in Los Angeles County, evacuation advisories and orders were issued for regions recently devastated by the Eaton fire, which burnt more than 14,000 acres and damaged over 9,400 houses. On Thursday morning, some Sierra Madre, Calif., residents were advised to leave before the storm hit.