Weather forecast

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The importance of weather in the mountains

It is a well-known fact that numerous accidents in the mountains occur due to adverse weather conditions. For this reason, it is really important to have some knowledge of meteorology.

If it is a good habit to consult weather reports even for a peaceful walk in the woods or on the green alpine meadows, it is even more important when facing challenging climbs or via ferratas. In the mountains, short-term forecasts have good reliability, unlike long-term forecasts. Other useful real-time indications are given to us by webcams, tools that are becoming increasingly widespread.

However, we all know that the weather in the mountains can change rapidly and abruptly, especially in summer. Therefore, we should not blindly rely on weather reports, and some basic knowledge of meteorology in the mountains should not be missing for those who frequent it.

The following is intended to provide some rudiments of meteorology, but they certainly cannot replace a good book that deals with meteorological phenomena. However, there are some warning signs that can be well interpreted and that it is useful to know.

How to understand if the weather is changing?

Talking about the weather in the Dolomites, there are some basic signs that warn us if the weather is changing. When medium or large cumulus clouds form in the sky, with developed protuberances in a vertical sense (typical cauliflower-shaped clouds), and maybe the day in the valley is hot and humid, it is almost certain that a thunderstorm will arrive in the following hours.

Also, the presence of small and harmless cumulus clouds (the classic fluffy clouds that only develop around noon and in the afternoon on stable weather days and are then called “fair weather cumulus”) at the beginning or in the middle of the morning can be a sign that the weather may deteriorate in the next few hours.

Sudden gusts of wind are also a sign not to be ignored, and it is good practice to keep an eye on the sky. It may also happen that we cannot perceive these signs. Perhaps we are climbing on a wall exposed to the south that precludes us from seeing the north-facing slope, on the opposite side of the mountain.

Dolomites weather: thunderstorms and lightning in the mountains

If lightning and/or thunder start, the motto is “if you can see it, hurry up, if you can hear it, run.” In fact, lightning can be visible even tens of kilometers away, while thunder can only be heard up to a few kilometers, a sign of an approaching thunderstorm.

The time interval between the flash of lightning and the rumble of thunder provides a measure of how close the thunderstorm is. An interval of 3 seconds between a flash and thunder means that the thunderstorm is 1000 meters away.

If you are interested in learning more about this phenomenon and the importance of being informed about the weather in the Dolomites, this website has a page dedicated to thunderstorms and lightning in the mountains.

Now let’s move on to the clouds. The shape of the clouds is a parameter to consider to interpret the evolution of weather conditions.

Observing the sky and clouds

SHAPE OF CLOUDS	MEANING
High and isolated clouds	Stability
Unaggregated clouds	Not dangerous
Aggregated clouds	Worsening
Cirrus - hooked - coming from the southwest	Imminent precipitation
Cirrus coming from the northeast and northwest	Stable, cold and clear weather
Cumulus clouds evolving during the day	Stability, good weather
Cumulus clouds evolving rapidly	Possible development of a thunderstorm
Cumulus clouds that do not disappear in the evening and aggregate	Weather is worsening
The Altocumulus_castellanus clouds	Atmospheric turbulence, possible thunderstorms
Altocumulus clouds that aggregate to form the so-called "sheepback" sky	Possible imminent rainfall, especially during the summer

The atmospheric pressure

Air has its own weight, and therefore the pressure it exerts on the surface of our planet can be measured. Without going into detail, it is enough to know that high pressure indicates good weather, while low pressure corresponds to worse weather. Atmospheric pressure is inversely proportional to the temperature of the air: in fact, it decreases with increasing temperature, because heating causes expansion and a consequent decrease in density in the atmosphere. Conversely, when air cools, density increases, and so does atmospheric pressure. Sudden variations in pressure values indicate an imminent change in weather conditions. In general, an increase in pressure indicates an improvement in weather conditions, while a decrease in pressure can anticipate a future worsening.

Barometric altimeter and meteorology

The barometric altimeter is a really useful tool that is based on atmospheric pressure. It can provide, in addition to data related to altitude above sea level, valuable information on atmospheric pressure and impending weather changes. If we stop at a certain altitude for a sufficiently long time (e.g. overnight in a mountain hut) and the altimeter indicates a significant change in altitude, then there is certainly a change in the weather, because the apparent change in altitude is actually due to a change in atmospheric pressure.

In particular:

• when the altimeter indicates a lower altitude than the actual altitude, there is high pressure and the weather will improve;
• if, on the other hand, the altitude has increased, there is low pressure and the weather will worsen.

Another example: if you reach a summit after a hike and the altitude indicated by the altimeter is higher than the actual altitude, it means that the atmospheric pressure is low, so the weather could worsen. If, on the other hand, the indicated altitude is lower than the actual one, then the pressure is high and some atmospheric stability can be expected.

Note Obviously, an altimeter that works based on a satellite navigation system will not be of any help in assessing possible weather changes. I am referring primarily to altimeters inserted in many watches that are based on position (GPS).

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