A later stage is reached when the hard crust is softened to a depth of about two or three inches (Telemark crust). This again gives good running.
Either before or after midday, according to altitude and inclination, all traces of crust disappear, and all slopes at moderate altitudes are reduced to wet, heavy and more or less water-logged snow. In the early spring this stage is perhaps only reached on southern slopes. In the late spring it is reached on all slopes at low altitudes and on north slopes, save, perhaps, at very high altitudes. In general, the ski-runner should not be abroad at such hours. Towards evening the slopes begin to refreeze. There may be an interval of hypo snow—soft hypo-like crystals in which fast running and every kind of swing is perfectly safe and easy. This is soon followed by the formation of a soft breakable crust, which gradually hardens until at last the cycle is complete by the formation of a hard solid crust.
Thus in general there are two periods of a spring day when ski-ing is easy, fast and safe. The first period is when the hard crust begins to soften, and the second period is when the wet melted snow begins to freeze. The ski-ing is least pleasant and most dangerous between midday and sunset.
The Effect of Föhn and Thaw
So far we have discussed normal winter and spring conditions. Föhn is, unfortunately, associated not only with spring but with winter. The conditions that are produced by Föhn are, however, spring conditions rather than winter conditions; for Föhn, though by no means uncommon in winter, is at least abnormal, whereas periods, more or less prolonged, of Föhn weather may be regarded as normal in spring. The peasants have a saying that, if the Föhn did not blow, the good God and the warm sun could do little with the snow. Certainly but for Föhn Switzerland would still be covered with glaciers.
Föhn, strictly speaking, should be used only for the warm dry wind that blows from the south, and which has been the cause of so many fires. The fire of Grindelwald was caused by this type of Föhn. The wind dries up the wooden chalets, and a spark from a cigar or a kitchen fire, carried on the wind, is enough to kindle wooden buildings from which the wind has absorbed every trace of moisture. But the word Föhn is also used for the warm, damp south-west wind, which is in every way utterly different from dry Föhn. They are alike only in that both dry and wet Föhn raise the temperature and melt the snow.
I propose to call the true Föhn Dry Föhn and the wet, warm south-west wind Wet Föhn.
Dry Föhn is often associated with long spells of warm dry weather. The skies are cloudless, and there is no hint of rain to be seen. You know that there is Föhn in the air by a peculiar warm dryness, a marked absence of coolness and moisture in the atmosphere.
The wet Föhn always brings rain. Sometimes dry and wet Föhn will fight for the mastery. Sometimes dry Föhn will emerge into wet Föhn and bring down the rain, only to recover its mastery a day or two later.
Föhn in Winter.