I was looking around at the blogs on Runner's World and I found a really cool "calculator" - What to Wear for Runners. You input temperature, wind, conditions and what you like to feel like when you run and it outputs suggested clothing items.
I put in the conditions for Sunday (45F, sun, no wind, feel cool) and it came back with what I plan to wear (almost). I am wearing a running skirt (it suggested shorts), long sleeve shirt, and sunglasses. I am skipping the hat that is suggested; I've never worn one running so I don't plan on trying it out on race day.
I added the link to the sidebar because I know I'll use it again.