A cold and wet storm is coiled in the Gulf of Alaska, and it will hurl snow and rain into Southern California late this week, forecasters said.
The cold low-pressure system will affect the region starting Wednesday afternoon, and last through Friday afternoon, National Weather Service forecasters said.
That will be an abrupt change from the warm and somewhat uneventful weather the region can expect early in the week, they said.
Forecasters expect a 20 percent chance of rainfall Wednesday evening in the Arcadia area, according to the NWS. That will rise to 50 percent Thursday.
The storm was expected to be stronger in San Diego County than in the Los Angeles area, forecasters in the Oxnard forecast office said. Light to moderate showers will start over mountains Wednesday afternoon, spreading to the flatlands along the coast by Wednesday night.
Snow levels will start between 4,000 and 4,500 feet above sea level, and then drop to as low as 3,500 in some places, the forecast said. That may be low enough to affect Interstate 5 over the Grapevine, Route 14 near Acton, Interstate 15 in Cajon Pass and Interstate 8 east of Alpine.
Thunderstorms will be possible Thursday afternoon, as cold and unstable air moves in above the clouds, the NWS said in a special weather statement issued in San Diego.
Rain will be variable, but about a half inch could be likely on the San Diego County coast and in the valleys. More than one inch of precipitation in the mountains is likely, some of it in the form of about 5 inches of snow above the 5,000-foot level.