Storms in the mountains
As the summer season approaches, the risk of thunderstorms in the mountains increases progressively. The hiker, the trekker, the mountaineer, the biker know very well that the storm is often accompanied by lightning. Just lightning represents the greatest danger for those who are outdoors in the midst of a summer storm. But before we talk about lightning, let’s see what the main types of storms are and how they are formed.
First of all, thunderstorms can be divided into two main categories:
Cold front storms. It happens when the cold air of the front, denser and heavier, is wedged under the pre-existing hot air, raising it abruptly. The cold front in summer often comes unexpectedly because the cloudiness induced by the hot front that precedes it is not even noticed that much, if not for a thin veiling of the sky. The passage of the cold front can also trigger intense thunderstorms (hail, heavy rain showers with lightning and thunder) accompanied by a temperature drop and by wind reinforcement. The frontal storms being phenomena linked to real fronts (perturbations) are easily predictable.
Heat storms or convection heaters. Usually they occur in the late afternoon or in the evening because they are linked to the strong heating of the air near the ground due to the strong sunshine. The hot and humid air bubble rising (breezes) meets cooler air which favors raising and consequent condensation in clouds. Thus the first mounds began to form and then, as the hours passed, they matured into real thunderclouds. Heat storms are mostly localized phenomena and generally run out in 30-60 minutes. This type of storm is hardly predictable well in advance. Important for the development of these storms is the degree of humidity present in the air: in the presence of very dry air the development of thermoconvective clouds does not take place.
How thunderstorms are formed
To have a thunderstorm it is not enough that there are clouds in the sky but these clouds must be cumulonimbus clouds. The cumulonimbus is the typical thundercloud with a vertical development (the base of these clouds starts from the lowest levels between 1000 and 2000 meters sometimes going up to 10.000-12.000 meters). The cumulus is in its ripening phase with characteristic cauliflower-shaped protuberances with very sharp contours.
The life of a cumulonimbus crosses mainly three stages:
normally at the beginning the heap comes to life due to a warm and moist air lift. This hot-humid current that “feeds” the cloud from below is called an inflow. The more the atmosphere is moist and unstable, the more the storm cloud formation will be favored. The cloud at the initial stage of development will still look harmless but will soon turn into a towering mound with sharp outlines. In this phase the precipitations are still absent.
In the central phase the full development of the temporal takes place. Within the thundercloud, in addition to the ascending currents, downward currents also begin to form. The highest part of the cloud widens and takes on a characteristic anvil shape while the base becomes progressively darker. On the ground, strong gusts of wind and ever closer thunder announce the arrival of rain. Then suddenly the first heavy rain showers arrive, sometimes accompanied by hail.
The final phase of “exhaustion” within the cloud is less the upward currents that feed the storm. Precipitation decreases in intensity. The storm cell tends to fray and rainfall becomes more and more residual
Warning signs of a thunderstorm in the mountains
- Presence of small turret clouds already early in the morning, the so-called “storm sheep”
- Absence of breezes and wind
- Humid and sultry atmosphere
- The piles do not remain isolated but tend to “organize” invading large portions of the sky.
- The clouds show increasingly clear protuberances as the hours go by
- Clouds at different heights and slowly rising up the sides of the mountains (presence of convective movements with colder air at high altitude)
- storms in the mountains
- Diagram of the various types of clouds with different heights
- Thunderstorms in the mountains and lightning risk
As anticipated at the beginning of the article the greatest danger for those who find themselves on a mountain path (worse if on the wall / via ferrata) while a storm breaks out is constituted by lightning. Lightning is an electrical discharge arising due to the difference in potential between the upper and lower parts of a cloud, or between two nearby clouds. Lightning emits a lot of light in a very long time frame