The atmosphere is a gaseous body in which, besides the gas molecules, there are suspended
molecules of water in the form of vapour. The atmosphere is subject to solar radiation which, over the course of the day and of the seasons, changes its temperature. Since the atmosphere behaves like any other gaseous body, it is subject to variations in pressure, which are closely related to temperature.
When two areas of the atmosphere with different temperatures and pressures meet, they begin to exchange masses of air, setting off the formation of winds. More precisely, the low-pressure area begins to suck in air from the high-pressure area, and more particularly the cold air, being heavier, slides under the warm air, which is more rarefied and consequently lighter.
Air masses can move on two planes at the same time: on a vertical plane, as in the case of cold air creeping in under masses of warm air, and horizontally, producing circular motions.
Besides the winds that arise from the meeting of high- and low-pressure masses, there are winds that develop over the twenty-four hours of a single day.
The principle, which we explain briefly here, is in any case fairly simple. The rocky slopes of the mountain, exposed to the morning sun, tend to warm up more quickly than the meadows on the valley floor (which stay in the shade longer). The air in contact with the slope warms up, becoming more rarefied and lighter. The result is that the warm air starts to rise. Through the suction effect, the cold air on the valley floor tends to rise, giving rise to what is normally called the “valley breeze”. The winds coming from the valley floor tend to die down as the hours go by, until in the early afternoon
a rather pleasant calm seems to settle over the mountains. When, on the other hand, the slope cools in the evening, the air too tends to become colder, compressing and becoming heavier: the air begins to sink down to the valley floor. Here on the valley floor the air that had warmed up during the day tends to rise, making way for the cold air.
Despite these theories, bear in mind that each mountain area lives by its own particular microclimate, and this rule is not always respected on every side of a mountain.
A good practice is to get to know the movement of air masses starting from concrete observation of the prevailing winds and of those that arise over the 24 hours. In summer, to understand where the prevailing winds come from, it is enough to examine the vegetation, the crowns of the trees and the shrubs. In winter, on the other hand, it will already be a good thing to observe where the snow cornices have formed.
Lastly, it is useful to ask the local people which are the main winds of the area; this can in fact turn out to be the best way to understand the movements of the wind in the place you intend to explore, as well as to make some new friends.
Up high the wind lowers the perceived temperature: find out about the wind chill effect.