I try to avoid rainy days because it's just not fun.
I try to avoid days below 50, but 40 is my minimum. Under 40 and it's just miserable for me. (Props to those of you who can deal with freezing temps. I'm not you.)
I often have things I need to do at lunch or after work that requires driving. So those days I can't do it.
And sometimes I wake up and just don't feel like it.
In the summer I average about 3 days a week. In the winter, 1 day a week.