Forgive me I just got my car, so I am still learning. After reading the manual and this blog and the fact that we are in the 21st century to me the Winter Mode setting is nuts. Cars equipped with the battery warmer should be "smart" enough to set the "winter mode" on/off when needed to maximize range, charge ability in cold weather, etc. To ask owners to worry about this setting is crazy. There are already too many bells end whistles on this car.
My suggestion is to set Winter Mode ON and forget about it. If the car is equipped with battery warmer and the sensors(s) work correctly, it should do nothing in the summer anyway.