A cold weather system that brought light showers early Thursday might be followed by a stronger storm that could bring snow to the mountains and more rain across the region.
Snow flurries are possible at the 3,000-foot level. Temperatures are forecast to drop up to 20 degrees below normal.
Radar showed a wide band of showers stretching from northern Los Angeles County to San Diego Thursday morning, but most of the shower activity came to an end by noon. Facebook visitors reported rain Thursday morning in Rancho Cucamonga, Santa Monica, Culver City, Huntington Beach, Moreno Valley and West Covina.
Showers might return Thursday night and extend into Friday morning.
"There's a bigger storm system that will arrive later on tonight," said NBC4 forecaster Elita Loresca. "We may not see a steady rain, but there may be some drizzle in some spots."
Rainfall amounts are difficult to forecast with precision because of the showery nature of the precipitation, according to NWS forecasters, who said they generally expect a quarter-inch of rain or less but that up to a third of an inch is possible.
The snow level will be at between 5,500 and 6,500 feet Thursday night but drop to between 4,000 and 4,500 feet during the day Friday and to between 3,000 and 3,500 feet Friday night, according to the advisory.
There may also be snow showers in the foothills above the Antelope Valley, but without accumulation.
The weather service warned motorists planning to travel through mountain areas to be prepared for snow showers, reduced visibility, icy roads and sharply colder temperatures.
The NWS forecast highs today of 52 on Mount Wilson; 60 in Saugus; 61 in Avalon, Burbank, and San Gabriel; 62 in Pasadena, Woodland Hills and downtown L.A.; 63 in Lancaster, Long Beach and at at LAX; 64 in Palmdale; 67 in Newport Beach; and 68 in Anaheim.
Several single-vehicle crashes -- including one on each side of the 110 Freeway at Manchester Boulevard -- were reported early Thursday, slowing the morning commute.