Storm forecast intensifies; flooding, mudflows possible

Evacuation warnings were slated for L.A. County as inclement weather approached.

- BY RONG-GONG LIN II AND CLARA HARTER

ROBERT GAUTHIER Los Angeles Times

Evacuation warnings were set to go into effect across Los Angeles County on Thursday evening as an atmospheric river approached Southern California, bringing with it the potential to put an early end to fire season while also bringing fresh risks of flooding and mudslides.

Under the storm scenario deemed most likely by forecasters, downtown L.A. would see 2.62 inches of rain Friday morning through Sunday, according to the National Weather Service. That could be enough to flood roads, swell rivers and creeks and cause minor shallow debris flows.

Rain of that extent would also make this L.A.'s wettest November in 40 years. And there's a 30% chance of even higher precipitation — 4.81 inches over the same time period for downtown L.A.

GENARO MOLINA Los Angeles Times L.A. COUNTY worker Pablo Castellano, top, helps prepare sand bags Thursday as Altadena residents line up to get them. In Malibu, a worker crosses Topanga Canyon Boulevard last month. The road was closed due to possible mudslides.

That would raise the possibility of significant mud and debris flows, as well as localized flooding of homes and businesses.

There's also a 10% chance that just about 1.4 inches of rain could fall downtown, which would result in only minor problems.

The day of highest risk is Saturday. For that day, "the main message is that there's still a pretty substantial potential for heavy rain over parts of our area, with a reasonable risk for flash flooding and debris flows," said Ryan Kittell, a meteorologist with the National Weather Service office in Oxnard. Debris flows are a type of landslide in which rainfall combines with mud and debris to move with destructive potential off hill sides.