I am attending my son's wedding in October, possibly outdoors in Napa Valley, CA. What is appropriate attire for business casual?

It can get chilly there in the evenings in October, if the wedding is an evening one. How about a dress with a matching light jacket?

I'm curious about the business part? They are getting married at work?
I agree about the dress with a little jacket. No lace or frills, a medium solid color, not pastel but not too dark either.