I have the same dilemma. Wind, rain, fog all affect how cold or hot I feel.
I went out for a run in a ss top and a running skirt. I got to my mailbox and it started raining. Well, sprinkling. Given the forecast is for this off and on stuff all day, I turned back and decided to go to the gym. It was 65 out and the rain felt cold... maybe if it was 75-80 I could run in the rain and not feel chilled.
My best suggestion is things you can layer/take off and a rain jacket small enough to put away in a bag. I also wear Craft sleeveless base layers, which make a big difference on days like today. It really warms your core.