Rain fell on the Southland Thursday and forecasters expect more over the weekend.
Main impacts will be hydroplaning on the freeways due to oil being lifted by the first rain in a long time," warned a National Weather Service advisory.
Tonight, the National Weather Service predicts more rain, mainly after 4 a.m. NWS expects Monrovia will have a low of around 52 degrees Friday with a 90 percent chance of rain.
Weather Service forecasters also warned of the possibility of urban flooding in low-lying areas of Los Angeles and Ventura counties.
The wet weather, resulting from subtropical moisture drifting north from Baja California and combining with a trough of low pressure, is expected to persist through Sunday, according to the National Weather Service.
There could be between a half-inch and three-quarters of an inch of rain along the coast and in the valleys, and up to to two inches in some parts of the San Gabriel Mountains, said Weather Service meteorologist Curt Kaplan.
The snow level, meanwhile, will remain high, falling to 6,000 feet in the San Gabriels by Friday evening and coming down some more Sunday, when some travel issues could arise on the Interstate 5 corridor even though little is expected in the way of rain or snow accumulation, Weather forecasters said.