In looking at my latest version of the w'w' vs wind direction plot, I see that I didn't site S15 in the best location. For wind directions from the NNE (one of the preferred directions to observe tower wakes), the flow at S15 appears to be influenced by the high ground/clump of trees to its North. I found that this plot was much better behaved when I used S8 as the reference. I'll keep on looking at this issue...