Summary of Winter Snow.
Winter snow may therefore be summarized as follows. The normal winter snow which is found throughout the winter on northern slopes and occasionally on southern slopes is powder snow which is perhaps the ideal ski-ing snow.
Powder snow deteriorates under the influence of wind and sun. Wind is the more mischievous. A little wind does no great harm, and the expert can even ski with pleasure on the hard crust formed by wind, but the extreme action of wind often produces varieties of snow which are all but unskiable.
The High Alps and lofty summits in general being most exposed to wind will usually yield inferior ski-ing to sheltered slopes. The best ski-ing in winter will therefore seldom be found on the glaciers.
Snow also deteriorates under the influence of sun, which forms a crust. This crust, however, once formed is often improved by a further dose of sun.
Though the best ski-ing is usually obtained on north slopes, excellent ski-ing is often obtained on south slopes by those whose knowledge of snow craft is sufficient to time their descent and to choose their route accurately.
Abnormal conditions produced by Föhn and thaw are dealt with on pp. [417-422].
Spring Snow
We have seen that good ski-ing in winter depends largely on the absence of wind. A sudden thaw may also produce a disastrous result, for snow which has once been rained on and refrozen will remain covered with crust until there is a new snowfall.
The best winter snow is without rival, but spring snow is, on the whole, safer and less capricious. In normal spring weather all snow is crusted in the early morning, for the sun is powerful enough to melt snow even on northern slopes. But this spring crust, as we shall soon show, is much less troublesome than crust in winter and yields very fine ski-ing indeed. Wind, the great enemy in winter, has no effect in spring, for wind cannot affect hard crust, and if wind blows while the snow is falling a few days of strong sun will melt any wind-formed crust and produce exactly the same surface as if the snow had never been touched by wind. It should, however, be added that, in the early spring, wind, though powerless on snow which has once been melted and crusted, is a great nuisance if it blows on snow which is still powdery, as is usually the case for twenty-four hours or so after a snowfall; snow which has once been crusted by the wind has a very strong resisting power to the action of the sun; I have known south snow in March retain irritating effects of wind action after several days of strong sun that would have been sufficiently potent to melt any ordinary crust.