Snow levels will hover around 4,500 feet Friday morning before falling to about 3,000 feet later in the day. The heaviest snowfall – as much as 10 inches in the higher elevation coastal slopes – is expected during the day Friday.
Residents can expect 6 to 10 inches of snow above 4,000 feet, said NBC4 forecaster Elita Loresca.
"Around noon-time today, it looks like that's when the wet weather will start to move in," Loresca said. "We're looking at a rain and snow mix."
The snow is expected to taper off into showers Friday night into Saturday, but cold temperatures are forecasted to continue for several nights, creating the potential for black ice and slippery roads.
The warning is in effect until 3 a.m. Saturday for Riverside County, and until 10 p.m. Friday for San Bernardino County.
Motorists in affected areas were warned only to venture out if it’s an emergency. If residents must drive in the storm, they are advised to bring a flashlight, food and water just in case.
The following areas of Riverside County are affected: Aguanga, Anza, Garner Valley, Idyllwild, Mountain Center, Pine Cove, Pinyon Pines, Vista Grande, Boulevard, Cameron, Campo, Cuyamaca, Descanso, Julian, Lake Henshaw, Moreno Village, Mount Laguna, Oak Grove, Pine Hills, Pine Valley, Ranchita, Santa Ysabel and Warner Springs.
These areas of San Bernardino County are affected: Angelus Oaks, Baldwin Lake, Barton Flats, Big Bear City, Big Bear Lake, Crestline, Fawnskin, Forest Falls, Interstate 15 at Cajon Summit, Laker Arrowhead, Mount Baldy, Mountain Home Village, Oak Glen, Phelan, Running Springs, Twin Peaks and Wrightwood.
Parts of Los Angeles County are under a winter weather advisory which began at midnight Friday and will last until noon Saturday, according to NWS.
Up to 8 inches of snow is expected to fall above 4,000 feet. And 4 inches or less is expected to coat mountain roads below 4,000 feet.
The storm could prompt the closures of Interstate 5 between Castaic and the Grapevine, and Highway 33 through the Ventura County Mountains, the weather service reported.
Wind advisories were also issued for several areas of Southern California.