Southern California (or SoCal as it is sometimes called) is known for its mild and pleasant weather, especially the winters. The region is dry and mild. However, there is a difference in climate between the coastal region and the inland region.
The coastal region, streching from about Santa Barbara in the north to San Diego in the south and averaging no more than 35 miles eastward from the Pacific Ocean, is generally touted as having the most pleasant weather in the USA -outside of Hawaii that is. In this long but narrow strip, summer daytime highs are mostly comfortable, but with variations. For example, during the month of July, Santa Monica averages daytime highs of 75(F) while Los Angeles averages daytime highs of 84(F). There may be occasional heat spells thrown in, but the summers are generally pleasant never-the-less. During the winter, daytime highs are usually in the mid-60s(F) for the entire coastal region, with occassional low 70s(F) temperatures thrown in. Year-round outdoor activities can be enjoyed day or night on the coastal region due to the mild climate that is dominated by Mediterranean-type weather.
The large inland section (which generally begins about 35 miles inland from the coast and stretches all the way eastward to the Arizona and Nevada borders) enjoys mild daytime winter temperatures, but the winter nights are chillier than the coastal region. Summer highs in the inland portion can be extremely hot. For example, during the month of July, daytime temperatures in Rancho Cucamonga average 91(F). For Palm Springs the average is 108(F). Summer nights are generally pleasant in much of the inland region.
Most rain and fog comes between mid-November through the end of March for Southern California, and sunshine is a stable throughout much of the year.