This time of year is considered our "dry" season. When we get rain it is typically tied to weather fronts, and it can last anywhere from a few hours to several days, depending on how fast the front clears the area. Most of the time it is not heavy rain like the summer storms - more of a drizzly light to medium rain. It's also harder to predict, so I would agree not to look more than a couple days out. Temps will be all over the place - cool when a front goes through, then heating up until the next one goes through. It can be 50 one day and 80 the next.
As far as jackets vs. sweatshirts, that will depend on whether it's windy or not. A jacket does a lot better job of blocking a cold wind than a sweatshirt. I usually bring a light jacket and a hoodie I can wear separately or together if necessary. Layers are always a good idea.