I read that. You did seem to have the thermocline dialed in for most of the summer. You also noticed a change. Surface water temps dropped significantly. Visible thermocline no longer present on your graph. I truly think some "mixing" has begun to take place. Maybe not a full fledged turnover, but things are changing for sure.
My fishing experience, around here, with the turnover, is brownish water color and a noticible odor. Some bottom debris floating on the surface and the bite is all but shut down for a couple weeks. Wind blown banks and pockets seem to accumulate more oxygenated water but the bite is still way off.
I am a retired Operations Supervisor in the Drinking Water Treatment Industry and my professional experience with the turnover is one of taste and odor related water quality issues, as well as, high raw water turbidity issues. Some years it would arrive sooner than later, usually sometime in mid/late October to early November. Maybe a call to your local water authority could help you fine tune your understanding? Anyway's, sorry for rambling and I do enjoy reading your posts.