Why does snow only remain on the north side of these trees? I've long been fascinated by microclimates, and once wrote a book (Frost Hollows and Other Microclimates, 1981). Some early-in-the-book text: "Once you begin to investigate little climates, you may find that the climate varies between one side of a house and another, between one side of a tree and another, and even between one side of a leaf and another." Microclimates are often important factors in location of vineyards and ski slopes, not to mention architecture and highway safety. And, near the book's end there is this: "Even the human body has a range of little climates. A Scientific American article titled "Life on the Human Skin" referred to 'the desert of the forearm, the cool woods of the scalp, and the tropical forest of the armpit. Consider the fungi that normally lives between human toes and is not noticed. Occasionally it multiplies and becomes an itching, irritating infection. It is called 'athlete's foot.' No one ever has to worry about an outbreak of 'athlete's elbow' or 'athlete's earlobe,' because the fungi needs the special human microclimate it finds between the toes."