A strong end-of-season storm is expected to bring significant and unreasonable amounts of precipitation to southern California from Sunday through the middle of next week, the National Weather Service said.
The system will be “similar to a February storm in April,” said meteorologist Joe Sirard. Winter storm watch is in effect for local mountains from late Sunday to Tuesday afternoon.
The rain will move to San Luis Obispo County late Saturday evening and will spread over the rest of southern California on Sunday. A more abundant precipitation band will move from Ventura County on Sunday evening to L.A. County on Monday.
The precipitation with this storm in many areas could exceed what is normally received for the entire month of April. In downtown Los Angeles, for example, normal April precipitation is 0.91 inches. But total precipitation until Tuesday could range from 1 to 2 inches in coastal areas and valleys, and 1.5 to 3 inches in foothills and mountains. Some mountain locations could see up to 4 inches.
There is also a slight risk of thunderstorms from Sunday evening to Tuesday evening. Any thunderstorm that develops could produce gusty winds, small hail and a dangerous cloud-to-ground flash.
Precipitation rates of a quarter to a half inch per hour are expected, but up to three quarters of an inch per hour are possible locally. Rates could be higher if there are thunderstorms that produce brief showers.
This means that minor debris and mudslides cannot be excluded in recently burnt areas.
Snow levels will start on Sunday between 6,000 and 6,500 feet, then fall from 5,000 to 5,500 feet on Monday. But early Tuesday morning, as the upper-low cold approached, snow levels would drop to 4,000 to 4,500 feet. Snow and wind could cause travel problems on Interstate 5 above the Grapevine. Winds could blow 45 to 60 mph at higher altitudes, and accumulations of 1 to 2 feet or more of snow are possible above 5500 feet.
After the dry months of January and February, then a disappointing March, early April behaves more like a winter month when this cold low pressure system arrives from the Gulf of Alaska. The depression was off the coast of Washington on Saturday afternoon and is expected to move south along the west coast to a position off the north coast of California on Sunday evening. Tuesday, the depression will settle off Point Conception, where it should become almost stationary.
The low system is expected to attract a plume of moisture from the North Pacific to produce significant precipitation. The most abundant rains, reinforced by a weak flow to the south, are expected on the slopes facing south and southwest in the mountains and foothills. The depression will tap into some subtropical humidity in the south, according to David Gomberg, a senior forecaster with the National Weather Service at Oxnard.
Rockfall on canyon roads and flooding of urban roads due to showers will no doubt make driving more difficult for those who have to go out, but this winter storm will also strongly encourage those who do not have to go to the cocoon at home and maintain the recommended social distance to slow the spread of the coronavirus.