Relentless rains from a series of atmospheric rivers are expected to take a “dead aim” at Los Angeles, with dangerous flooding, mudslides and debris flows possible in the region through Christmas, forecasters said.
Mike Wofford, a meteorologist at the Los Angeles office of the National Weather Service, said the heavy rain would arrive in two rounds. The first and most intense is expected to push into Southern California late Tuesday and to strengthen on Wednesday.
“And we’re expecting another round on Christmas Day,” he said. “Maybe not quite as heavy, but still periods of very heavy rain through Thursday as well.”
Where the Heaviest Rain Is Expected
The Weather Prediction Center has placed much of Southern California under a Level 3 out of 4 risk for flash flooding from Wednesday through Thursday. Portions of Los Angeles and Ventura Counties, including Downtown Los Angeles and the San Fernando and San Gabriel Valleys, are under a Level 4 out of 4 risk.
Forecasters expect coastal and valley areas to receive between three and six inches of rain by Christmas Day. Totals are expected to be significantly higher in the foothills and mountains, where five to 11 inches are forecast. Rainfall rates could reach 1.5 inches per hour.
Flood watches were in effect from Tuesday afternoon through Thursday evening for large swaths of Southern California and the central coast, including San Luis Obispo, Santa Barbara, Ventura and Los Angeles Counties.
Flooding, Winds and Other Hazards
Mr. Wofford said the deluges were expected to cause a range of hazards across the region.
“We’re going to see a lot of mudslides in our canyons, and there’s going to be a lot of clogged drains and a lot of standing water,” he said. “And in the mountains and in our burn areas, there’s a chance of seeing some debris flows, and just a lot of flooding overall in our urban areas.”
Strong winds are also expected starting Tuesday afternoon and continuing into early Wednesday, with wind gusts of 35 to 55 miles per hour forecast.
Gusts could reach up to 80 m.p.h. in Santa Barbara and San Luis Obispo Counties and the mountains and deserts of Ventura and Los Angeles Counties. High-wind warnings were issued for those areas starting at noon Tuesday and lasting through Thursday afternoon.
Forecasters warned that the combination of saturated soils and strong winds could topple trees and lead to power outages, especially in areas under high-wind warnings.
Thunderstorms are also expected, especially Tuesday night through Wednesday. The Storm Prediction Center said the storms could produce hail, strong wind gusts and possibly a tornado along the Central and Southern California coast and inland across the San Joaquin Valley.
Storms Return to Northern and Central California
The storms in Southern California are part of a broader system that has already drenched Northern and Central California since the weekend.
In Shasta County, heavy rain set off flash flooding on Sunday that killed at least one person, according to officials.
The next parade of storms is expected to continue pummeling central and northern parts of the state through Friday, renewing the risk of flooding.
In Northern California, valley areas could see between 1.5 and three inches of rain through Friday, while coastal and mountainous regions are forecast to receive four to eight inches. Some spots could get up to 10 inches.
Along the central coast — from northern Santa Barbara to San Francisco — rainfall totals of two to four inches are expected in coastal and valley areas, with up to seven inches possible in the foothills and mountains by Christmas Day.
Flood watches were in place across much of Northern and Central California, including the Sacramento Valley, northern San Joaquin Valley, the California Delta and the Sierra Nevada, through Friday afternoon.
Snow in the Sierras
In Northern California, forecasters said heavy snow could blanket all major Sierra Nevada mountain passes, with up to one foot of accumulation above elevations around 7,000 feet, and up to two feet of snow above elevations of 8,000 feet through Friday.
With strong winds also forecast, conditions in the high Sierra could make travel extremely difficult or even impossible at times with potential damage to infrastructure, forecasters said.
The wet and unsettled weather is expected to persist across California through Saturday.
Nazaneen Ghaffar is a Times reporter on the Weather team.
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