As a powerful Pacific storm rolls into Southern California, people are bracing for the possibility of life-threatening flooding, mudslides and debris flows, especially near the burn scars in the Los Angeles area.
A storm system moved through northern and central California on Thursday, bringing strong winds and heavy rain. Over the past 24 hours, widespread precipitation totals of 1 to 2 inches were observed along the coast, with isolated precipitation of 3 to 5 inches in the coastal mountains.
Nearly an inch and a half of rain fell in San Francisco on Thursday, nearly 75% of the November average. November transitions into the wet winter months, and December through February are the wettest months of the year in the Bay Area.
Winds were gusting between 60 and 80 mph in the highlands on Thursday, with gusts reaching 50 mph in San Francisco.
As it descends into Southern California, the winds will subside, but the threat of flooding will increase as atmospheric rivers funnel moisture from the ocean into the storm.
An early wave of heavy rain in Southern California has already caused flooding and mudslides along parts of Highway 101 in southern Santa Barbara County, according to the National Weather Service. This rain is expected to ease by Friday afternoon.
A stronger second wave is likely to move into the region from Friday night into Saturday, causing prolonged heavy rain. Rainfall can sometimes reach 1 inch per hour.
Much of the Los Angeles area is under a flood watch until Saturday at 10 p.m. The National Weather Service warns that the storm could cause life-threatening debris flows, leading to power outages and flooding of roads.
Burnt areas from recent wildfires in the region will be particularly vulnerable to landslides and debris flows. Wildfires not only destroy plants that normally absorb some of the rainfall, but their extreme heat can change the soil and form a water-repellent layer just below the surface.
Officials warned residents near the burn scars from the recent Palisades, Hearst and Sunset fires to prepare to evacuate.
“Residents, especially those in vulnerable areas, should take immediate precautions to prepare for the storm and protect their interests,” the National Weather Service in Los Angeles said. “This scenario could cause a number of significant impacts across the region, including debris flows in the fire area, significant water pooling on roads and highways, landslides through canyons, and downed trees.”
Residents can pick up sandbags at fire stations across the city, and sand is also available for free in some locations.
The heaviest rain should ease by late Saturday, but the region won’t see clear skies any time soon. Showers will continue into Sunday, leaving the ground soggy. It doesn’t take much rain to cause minor flooding or to keep roads smooth, especially in places where drainage is slow after a big storm.
