Yes, Desert Dwellers is right. SoCal in winter can be warm, it can be pouring rain - heavy, monsoon-like rain, or it can be very cold (for California) and dry. I have experienced all of these events.
Last December (12/19/10, to be exact), I had my winter coat stuffed in a locker in DL, ready to whip it out at a moment's notice because I was expecting that I would be freezing again by nighttime, as I had been in 2008. Not so. While the temperature dropped down to maybe the 50's or so, I was not cold enough to go get the coat, so I stayed in my t-shirt, with my arms exposed, for the entire night, until right before midnight. I was fine. It was probably in the upper 70's during the daytime.
In 2008, however, I was f-r-r-r-r-r-e-e-e-e-e-e-e-e-zing at night in DLR - like to the point where my teeth were chattering - and my coat was all the way back in the hotel room and not convenient for me to get.

It was in the 40's. This is coming from someone who hates heat and loves it when it gets cold!! (I still do - I like to bundle up to get warm rather than be uncomfortable in the heat.) But the next night, I made sure to bundle up in the winter coat, a bulky sweater and a neck scarf, with mittens at the ready. And the day after that, it was raining, so I had to bundle up and walk around DLR with an umbrella that stabbed my hand!
I have also been at DLR when it was only in the 40's in the daytime and about 30 degrees at night, and it was knit cap & earmuff weather, literally. My friends and I were totally covered in layers the entire day and night. It was freezing - but fun!!