Start by giving us some pics of your fall commute and posting them here

Also prime motivators of the ego-centric type:

D*** my legs are lookin' good ( especially when the lady(ies) comment)
I can eat what if I put in enough miles and still be trim

comfort:

It feels so good to be warm after ( just don't fall asleep at the job )
I feel so much better if I bike, terrible if I don't

aesthetics:

Generally it is a pleasant ride out in the fresh air, great smells, sights and sounds

humor:

Getting a kick out of other people's reactions who think I am crazy

economy:

Man it saves gas, especially in cold weather