An unusually strong storm system has reached Southern California, raising fears that the rain could unleash a threat that has been lingering in the burn scars of wildfires that ravaged Los Angeles communities in recent years.

Called debris flows, these fast-moving slurries of floodwater and sediment can hurtle down slopes carrying cars, trees and even boulders with them.

They’re like “a flood on steroids,” said Jason Kean, a research hydrologist with the U.S. Geological Survey’s landslide hazards program. “It’s really hard to stop these things. The best thing to do is get out of the way.”

Forecasters expect the heaviest rain Friday into Saturday night; predictions are for wet days through next week. Storms may stretch from Santa Barbara County south to Los Angeles County, and could sp

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