System bringing rain and snow is ‘similar to a February storm’

A powerful late-season storm is expected to bring significant and unseasonable 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. A winter storm watch is in effect for the local mountains from late Sunday through Tuesday afternoon.

Rain will move into San Luis Obispo County late Saturday night and spread over the rest of Southern California Sunday. A band of heavier precipitation will move from Ventura County on Sunday night into L.A. County on Monday.

Rainfall 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 rainfall for April is 0.91 of an inch. But rainfall totals through Tuesday could range from 1 to 2 inches in coastal and valley areas, and 1.5 to 3 inches in the foothills and mountains. Some mountain locations could see as much as 4 inches.

There is also a slight chance of thunderstorms Sunday night through Tuesday evening. Any thunderstorms that develop could produce gusty winds, small hail and dangerous cloud-to-ground lightning.

Rainfall 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 downpours.

That means minor debris and mud flows can’t be ruled out in recent burn areas.

Snow and blowing snow could interfere with travel over the Grapevine Tuesday morning.

(Paul Duginski / Los Angeles Times)

Snow levels will start out Sunday between 6,000 and 6,500 feet, then drop to 5,000 to 5,500 feet on Monday. But by early Tuesday morning, as the cold upper-low approaches, snow levels will dip to 4,000 to 4,500 feet. Snow and wind could cause travel issues on Interstate 5 over the Grapevine. Winds could gust from 45 to 60 mph at higher elevations, and accumulations of 1 to 2 feet of snow or more are possible above 5,500 feet.

The storm’s expected position on Tuesday.

(Paul Duginski / Los Angeles Times)

After the bone-dry months of January and February, then a disappointing March, early April is behaving more like a winter month as this cold low-pressure system arrives from the Gulf of Alaska. The low was off the Washington coast Saturday afternoon and is expected to move south along the West Coast to a position off the Northern California coast by late Sunday. By Tuesday, the low will settle off Point Conception, where it is expected to become nearly stationary.

The low system is expected to draw in a plume of moisture from the north Pacific to produce significant precipitation. The heaviest rainfall, enhanced by low-level southerly flow, is expected on south- and southwest-facing slopes in the mountains and foothills. The low will tap into some subtropical moisture to the south, according to David Gomberg, a lead forecaster with the National Weather Service in Oxnard.

Rock falls on canyon roads and urban roadway flooding from downpours will undoubtedly make driving more challenging for those who have to be out and about, but this wintry storm will also provide a strong incentive for those who don’t have to travel to cocoon at home and maintain the social distancing recommended to slow the spread of the coronavirus.