Los Angeles County could see between a quarter-inch and half-inch of rain Friday as the first of two anticipated storm systems passes through the region this weekend, according to the National Weather Service. The rainfall will add to what is already the wettest month recorded in downtown Los Angeles since December 2010, said David Sweet, a weather service meteorologist. So far this month, the area has seen 4 inches of rain, nearly double the historical average for December. On Friday, there’s an 80% chance of rain forecast at 4 a.m., with a possibility of showers returning Friday night, Sweet said.