The winter of the calendar ends officially on 23 March, and the calendar spring lasts from 24 March to 23 June. None the less March, whatever the calendar may say, is winter in the High Alps. The snow, unless disturbed by wind, remains powdery on all north slopes and gentle south slopes. March is often a month of snowstorms, though occasionally it is distinguished by really fine weather. On the whole, however, it cannot be said to be a good month for glacier ski-ing, though, on the other hand, the days are longer than in February. The sun is stronger and the crevasses more securely bridged.
April.
April marks the transition from winter to spring. As a rule, April is marked in the Alps by frequent storms, varied by periods of wet Föhn. Occasionally one gets a week of really good weather and fine ski-ing, even at very low altitudes, and it often happens that the last week in April is perfect succeeding to a long period of snowstorms. But as a rule good weather is less common in April than in any month of the alpine year.
The snow itself varies. Powder snow is found on north slopes at high altitudes. South slopes are usually crusted. The crust varies a great deal, and resembles, in general, the crust found in winter at low altitudes. In other words, April crust on the glaciers is usually marble crust in the early mornings. The law, explained on p. [414], “The milder the frost the better the crust,” often gives the clue to timing a successful descent. As one descends on an early morning in April the crust usually improves.
As a rule, the sun is strong enough to melt the crust just before or just after midday, and in this case you get perfect running on Telemark crust. Owing to the lower temperature the snow remains good much longer than in May. In fact, at high altitudes it seldom becomes completely thawed, so that the ski-ing on April afternoons is usually better than on May afternoons.
It is important to notice that when, as in spring and summer, the sun remains above the horizon after 6 p.m., the northern slopes will be in the sun after the southern slopes have lost the sun, for the sun at 6 p.m. is due west and after 6 p.m. is north of west. Of course, as the sun is low in the sky only north slopes that are not shut in by neighbouring slopes will keep the sun.
If a north wind is blowing, the snow on north slopes, previously crusted by sun and frost, may remain quite unmelted throughout the day. I have found hard slippery crust in the late afternoon at the end of April just below the rocks of the Zinal Rothhorn, with the result that the ski-ing was most unpleasant. A bitter north wind was blowing at the time. So, too, south slopes when the north wind is blowing may resist the sun, and though they will not, like north slopes, remain really hard, they will not be thoroughly melted.
If you are lucky enough to get fine weather, April ski-ing is often delightful. After a few days of sun traces of wind action disappear from all slopes, save perhaps north slopes at very high altitudes. Telemark crust towards midday, and even later, and salt snow or hypo snow (p. [417]) as you descend from the glaciers to the lower regions, are characteristic of April ski-ing.
It may be necessary to time your descent to the valley so as to pass a dangerous slope before the sun has struck it. With ordinary caution an experienced party should run no risk whatever of being caught by an avalanche; but it is undeniable that inexperienced parties come to grief more frequently in April than in any other month. This does not prove that the avalanche danger is really greater, but only that it is greater for the inexperienced.
May.