A new storm system will generate two days of rain, heavy snow and furious winds in the Southland starting today, prompting forecasters to issue a flash flood watch for the region.
The Pacific storm will first slam into Santa Barbara County and likely spread into Ventura and Los Angeles counties later this morning and this afternoon, according to an NWS advisory.
There is likely to be a "relative lull in the precipitation tonight" before more rain hits the Southland Saturday, when, amid unstable air, there also will be a "slight chance of thunderstorms," it said.
"Rainfall rates could locally exceed one half-inch per hour at times today through Saturday, especially across south-facing slopes and near thunderstorms," the advisory said.
Through Saturday, rainfall totals are generally expected to range between three-quarters and one and-a-half inch of rain across coastal and valley areas, with 2-4 inches possible in foothills and mountains, according to the NWS.
The NWS issued a flash flood watch – which means conditions conducive to flash flooding may develop – for Los Angeles County mountains, other than the Santa Monica range, and the San Fernando, Santa Clarita, San Gabriel and Pomona valleys.
The flood watch – which covers areas denuded by wildfire, including the site of the 250-square-mile Station Fire in the Los Angeles National Forest – will be in effect from noon today through Saturday afternoon.
"Residents in or below the recent burn areas are urged to take the steps necessary to protect their property," according to an NWS advisory.
The NWS also issued a winter storm warning, which will be into effect from noon today through 9 p.m. Saturday, for the mountains of Ventura and Los Angeles counties, other than the Santa Monicas. The warning reflects an expectation of heavy snow and high winds, making travel dangerous.
Initially, the snow level will remain high today – generally around 7,000 feet, though possibly 6,000 on north-facing slopes, according to the NWS.
But Saturday's snow level is expected to range between 4,500 and 5,000 feet, possibly affecting Interstate 5 travel in the area of The Grapevine, the NWS said in a winter weather advisory.
It said total snow accumulation of 12-20 inches is expected above 7,000 feet through Saturday, 6-12 inches between 6,000 and 7,000 feet.
"In addition to the potential for heavy snowfall, gusty southeast-to-south winds are expected today and tonight, with gusts to around 55 miles per hour possible," the advisory said.
"Motorists traveling across the higher resort areas should be prepared for the possibility of visibilities near zero at times due to the combination of blowing snow and dense fog."
The NWS forecast highs today of 48 on Mount Wilson; 55 in Palmdale and Lancaster; 57 in Newhall; 60 in Avalon; 61 in Pasadena, San Gabriel, Burbank, Woodland Hills and at LAX; 62 in Long Beach and Anaheim; and 63 in downtown L.A. and Newport Beach. Temperatures are expected to remain at roughly the same level through at least Thursday.