Many people consider it a good sign if the weather has been clear, cold and sunny for a period of time. However, cold and clear weather has two unfortunate influences on the stability of the snow. Firstly, cold and clear weather often results in the formation of frost that lies on the snow. After a period of time, a layer of fragile frost will be built up and can present a real danger, because it can easily collapse and become a slippery layer if a new layer of snow falls on top of it.

Secondly, a long period of very cold weather, results in a series of changes to the lowest layer of snow. Moisture from the lower levels pushes a few centimeters up through the layer of snow, and sets itself as ice crystals on top of the snowflakes. This results in what is called "swimming snow". You cannot see swimming snow on the surface. This type of snow is built up from within. The colder it is and the thinner the layer of snow there is, the faster swimming snow can be formed. This means that even though the outer layer of snow seems hard and reliable, an unstable layer of swimming snow can easily be hidden below the surface and can collapse under the weight of a skier.

In order to be able to judge this danger, you should follow the weather conditions carefully in the weeks leading up to your ski trip, and always ask the locals about the conditions when you arrive at the ski resort.