In re: short sleeves...
It's Southern California-cold, not anywhere-that-understands-cold-cold. LOL. It's weird, but we can have several feet of snow up there, and still spend the day in jeans and a tee shirt. I've skied there in short sleeve shirts, and, even after falling, as long as I didn't stand in the shade for too long in a wet shirt/jeans, I was just fine.
It's hard to explain what Southern California cold is to folks who know what "real" cold is. This is not it. I've been colder skydiving than I have been skiing.
I've been outside the state when it *is* cold - New York, Maine, Connecticut, Colorado, Washington, and even parts of Oregon. That is "real" cold. SoCa is kinda like "cold-lite". We pretend it's cold, and for those who don't know what real cold is it feels cold, but it's really not.
Best-
Herding Cats