Cut that tree branch! Nice practice area I must say.
Your analysis is pretty spot on. To my eyes, you are popping up when the club gets to about hip level or slightly higher on your backswing.
I've been studying Ben Hogan's swing as I learn, he covers the left wrist supination on the downswing, stating pretty plainly that to him all good golfers supinated the left wrist about like so on the downswing.