Anyone who has walked on a frigid Northwoods morning has heard the telltale squeak of snow underfoot. But why does this only happen when temperatures drop well below freezing? The answer lies in snow crystals. When freshly fallen snow is compressed, the ice grains rub against each other. At warmer temperatures, a thin layer of water between the grains allows for smooth movement. But in extreme cold, below about 14°F, the water layer disappears, causing the grains to grind together, producing the familiar high pitched squeak.