A “winter-like” storm will move into Southern California late Monday into Wednesday, bringing the chance for widespread, significant rainfall and locally damaging winds that could trigger flash floods, the National Weather Service warned Monday.
A flood watch has been issued for much of the region from Monday evening through Tuesday, particularly in areas in and around recent burn scars, including the footprint for the Eaton and Palisades fires.
The “potential for brief, heavy rainfall over the burn scars may trigger hazardous and damaging flooding and debris flows,” the advisory said. “Flooding may also occur in poor drainage and urban areas.”
Rainfall totals during that time could range from three-quarters of an inch to 1½ inches for most coastal and valley areas, said Richard Thompson, a meteorologist for the weather service. Mountain and foothill areas could see up to 3½ inches of rain.
Severe thunderstorms could also develop across the region, bringing the chance for locally heavy downpours, damaging winds up to 60 mph and some brief tornadoes and hail, the weather service warned. San Luis Obispo, Santa Barbara and Ventura counties were most likely to see those storms develop, with about a 20% chance in Los Angeles County.
Rainfall rates could reach up to seven-tenths of an inch per hour, which may be enough to trigger mud and debris flows over several recent burn scars, the Weather Service warned.
State and local officials were bracing for the unusually strong October storm. In a statement, Gov. Gavin Newsom said officials had pre-positioned resources in Southern California, including dozers, hand crews, rescue swimmers, and helicopters. Mayor Karen Bass said city departments “stand by to respond to any impacts.”
Farther north along the Central Coast and in the Central Sierra, inches of rain and feet of snow are expected through Tuesday night.
“Travel could be very difficult to impossible,” for parts of Yosemite, Kings and Sequoia national parks, the weather service warned.
Up to 4 inches of rain could also fall along south-facing slopes in the Santa Ynez Mountains in Santa Barbara County, according to the Weather Service’s forecast Monday morning.
Though it is early in the season, it’s not unheard of to get a storm or two in October, Thompson said.
“Usually our Octobers are dry,” he said, “but we do get storms from time to time.”
The early-season storm coincides with the official return of La Niña, a climate pattern that often drives drought in Southern California.
The reemergence of the ocean phenomenon — after last year’s rainfall was below average — increases the chances of another drier-than-average winter, further worsening fire conditions in the region.
It’s not yet clear how this week’s storm may throw off La Niña projections. Forecasters say it only takes one or two big storms in Southern California to buck projections for a dry season.
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