The climate for San Diego is mild. The weather in San Diego is wonderful! There is generally low humidity, even in summer. The temperature rarely falls below 40 degrees in the winter, making it a great place to spend the winter. Most of the rain falls between December and March. San Diego average annual rainfall is less than 10 inches per year San Diego average temperature is (Spring) 61, (Summer) 69, (Fall) 66, (Winter) 57 degrees F.