I live in Atlanta and wore both 13 oz and 16 oz kilts all winter comfortably. Same for winter trips to Memphis. Key are warm feet, hands, and torso/head. A 13 oz will be plenty warm enough for Nashville if you like the lighter weight generally. the waistband keeps your belly warm in winter, and that's a large part of your torso. I've also got no problem wearing 16-oz wool in 80-85 degree weather either (as long as the humidity is reasonable).