Thistle, our climates are similar, and I actually do what you describe -- not the hanger flipping, but the closet changeovers.
I do two BIG ones -- in fall, and spring. But I also do "mid" changeovers of certain items in the winter and summer. So....in winter I add my heavier weight sweaters (and may subtract a few of the shirts that won't get worn in the super cold temperatures). And in summer I add in the very light weight linens, etc. (and take away some of the heavier shirts, etc. and some of the sweaters that stayed during the spring.)
Using this system, with my relatively compact closet, I know exactly what I'm wearing and how often. The only things that don't get worn are things that don't fit right (I try to donate them quickly), things that I have few occasions for (dressy shoes, mostly, and a few dresses), and things that turn out to be poor fits for that year's weather patterns. That last category is hard to predict and I don't really blame myself for getting caught, occasionally. Our weather can be quite different year to year. One year the summer will be cool and I'll want sleeved tops; the next year it will be broiling and I'll need sleeveless.
I really noticed a few patterns over the past year that will help to govern my buying, going forward:
1. I wear knits almost exclusively in winter at home. All my warm knits get a ton of wear.
2. I wear woven tops in the spring, summer, and fall -- but much more rarely in winter.
3. I wear skirts and dresses far more in spring and summer. Almost never wear them in the winter.
4. I love jackets -- LOVE -- but only really wear them when I am on a city jaunt. Not so much for work at home. This means I probably need fewer of them than I might like to own.
