LOS ANGELES (AP) - An “atmospheric river” weather system dumped rain and snow on California on Thursday, and forecasters said another, stronger, plume of moisture from the Pacific Ocean would slam the state during the weekend.
An atmospheric river is a long and narrow region of the atmosphere that horizontally transports moisture out of the tropics, according to the National Oceanic and Atmospheric Administration. An atmospheric river that brings moisture to the West Coast from near Hawaii is sometimes called a “Pineapple Express.”
The system prompted heavy snow in the Sierra Nevada, where the Mammoth Mountain ski resort reported accumulations ranging from 44 inches to 7 feet in 1½ days, with more falling. The snowfall closed mountain routes or forced chain and snow tire requirements.
Torrential rain fell in some areas, including parts of Tulare and Kern counties, where flash flood warnings were in effect for much of the day after as much as 9 inches of rain fell, the National Weather Service said.,
On the Central Coast, more than 8 inches of rain fell at Rocky Butte in San Luis Obispo County. Rock slides closed Highway 1 from 11 miles north of San Simeon to about 4 miles south of Big Sur, the California Department of Transportation said.
Rainfall amounts across most of Southern California were much more modest but contributed to continuing relief after five years of drought. Hillsides covered in long-dead dead brush have turned from brown to green as January rains follow a wet December.
As of Thursday morning downtown, Los Angeles had nearly 6 inches of rain since the Oct. 1 start of the water year - well above normal to date and more than five times as much what fell by same time a year ago. A swift-water rescue team pulled a man off a brushy island in the Los Angeles River, which normally runs at a trickle until it swells with runoff.
The first atmospheric river event was expected to taper off Thursday night, followed by drying through Friday night.
This week’s second, wetter, atmospheric river was forecast to arrive in California Saturday morning and continue into Monday, bringing heavy snow to the Sierra Nevada above 9,000 feet and heavy rain in the Sierra and foothills below 8,000 feet.
Highest elevations of the Sierra can expect 3 feet to 6 feet of snow and some locations could get 8 feet, the weather service said.
Forecasters said potential hazards from the event could include flash flooding, mudslides, debris flows near recent wildfire burn scars and urban and small stream flooding in the San Joaquin Valley.
“It cannot be emphasized enough that the forecast amounts of rain will cause extreme flooding for the Sierra, foothills and adjacent lower elevations,” the Hanford weather office wrote. “Yosemite Park has the potential for a major flood as well as most other locations along rivers and streams in the Central California Interior.”
The National Park Service said visitors should be aware that Yosemite might close for several days due to predictions of significant rainfall and the Merced River rising well above flood stages.
A flood in January 1997 cause so much damage to roads, campgrounds, lodging and utilities that the park was closed until the following March.
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