The snow line is the line at which snow is continuously covering the ground. You can see it most clearly in mountain areas. In this picture you can see that the snow line is half way up the valley sides. During the spring, as the air becomes warmer, the snow will melt at lower levels and the area of cold air will only exist near the mountain tops. So during spring the snow line rises. In autumn it falls.

The snow line is important for animals, and for skiers. Few animals can find food under snow and so, as the snow line lowers in autumn, the animals have to migrate down the valley, or find somewhere to hibernate. In spring, they can move up the mountainsides as new plants are exposed.

The snow line is important for ski resorts. They need to be sited above the snow line for as much of the year as possible. Otherwise skiers will have to go to the pistes by bus and the resort will be less attractive.