Spring snow is quite common in winter when dry Föhn follows wet Föhn, and the wise ski-runner will seize every chance of securing spring conditions once he has despaired of proper winter conditions. He will choose south slopes instead of north slopes, low altitudes instead of high altitudes, and time his descent for the sunny rather than the shady hours. “The milder the frost the better the crust.” From which it follows that the lower the altitude and the drier the Föhn the better the ski-ing—once normal winter conditions have been interrupted.
It is most interesting to observe how the same slope will be composed of typical spring crust one day and of impossible slippery winter marble crust the next day. The difference is solely due to the fact that, in the first case, the night’s frost had been mild, and in the second case severe.
After Föhn you will often, for instance, find a queer kind of surface, called Foam crust, composed of innumerable overlapping edges, miniature cornices formed by a little trickle of water, a mere drop, which has run off a thin small eave of snow. Now hard frozen foam crust is very unpleasant, but directly the dry Föhn gains the mastery, and directly the hard foam crust is exposed to a hot sun and a hot dry Föhn atmosphere, it immediately softens, and yields very fine ski-ing not unlike the best Telemark crust.
To summarize the effect of Föhn in WINTER:
Wet Föhn followed by frosts produces a crust on all slopes which have been exposed to thaw. If the Föhn is very pronounced, and is accompanied by rain, which is followed by frost, all slopes will be covered by a hard solid crust.
If a period of normal cold winter weather sets in, this crust will be very hard and very slippery, and will only yield good ski-ing on south slopes exposed to the sun.
If the wet Föhn is followed by dry Föhn, you will get spring conditions at any rate at low altitudes—a hard crust, smoother but not unlike perforated crust, in the early morning, and a soft crust, not unlike Telemark crust, on south slopes when the sun is shining on them.
Föhn in Spring.
The Föhn is less deadly in spring, because snow which has been crusted by Föhn and frost is remelted by the sun, and the sun and frost together will always produce the same surface, whatever has gone before. A wind-swept slope or a Föhn-crusted slope are affected in precisely the same way. In winter Föhn spoils all snow that it has affected, and, save for the lucky accident of dry Föhn, one has to wait for a new fall till normal winter conditions are restored. But in spring, once the Föhn has ceased, a single sunny day followed by a single cold night’s frost is sufficient to produce the normal spring conditions, hard crust in the morning passing through the normal transformations of the spring day.
Wet Föhn is, however, most unpleasant in spring while it lasts. If you are caught by wet Föhn in a club hut you are imprisoned till the Föhn passes, for the wet Föhn brings down the avalanches on every slope above 23 degrees (see p. [430]). Ski-ing, while there is a touch of wet Föhn in the air, is always unpleasant. Snow which has been melted by the sun in a dry atmosphere never entirely loses its crystalline formation, excepting at low altitudes in the very late spring. And even then sun-melted snow is never so unpleasant as snow melted by the Föhn. The Föhn disintegrates the snow, destroys the crystalline formation, reduces the snow to one uniform heavy mass.