Thunderstorms in the mountains are not just an unpleasant weather event: they can become, within minutes, a real and immediate threat to life.
Every summer, hikers and climbers are exposed to lightning strikes because they underestimate the signs of the sky or believe they “still have time”. In the mountains, however, weather conditions can change very quickly, and when a thunderstorm arrives, it is often already too late to find a safe shelter.
Understanding how thunderstorms develop, recognizing early warning signs, and knowing how to behave can make the difference between a day that ends wet… and a much more serious situation.
Thunderstorms in the Dolomites
In the Dolomites, thunderstorms are typical of the warm season, roughly from June to September. During this period, there are on average 6–10 thunderstorm days per month, usually developing in the afternoon or early evening.
This pattern makes careful planning essential, especially for long or demanding mountain routes.
How to recognize an approaching thunderstorm
The arrival of a thunderstorm can often be anticipated by observing local weather conditions. Cloud build-up over the mountains can provide clues about the direction and evolution of a storm.
However, due to the irregular nature of cloud formation, it is not always possible to determine exactly where the thunderstorm will develop.
A simple and useful method is to count the time between seeing a lightning flash and hearing the thunder: 3 seconds correspond to approximately 1 km of distance.
In flat terrain, thunder can be heard up to 20 km away. In the mountains, sound propagation is often limited by surrounding peaks, and echoes can be misleading regarding both distance and intensity.
Why lightning is so dangerous in the mountains?
Lightning is an electrical discharge caused by a strong difference in electrical potential between clouds or between clouds and the ground. A lightning strike can reach lengths of up to 20 km.
Discharges between clouds are dangerous, especially when climbers are surrounded by clouds or fog. However, the greatest risk comes from cloud-to-ground lightning.
These strikes tend to hit summits, ridges, and high points, which are the most exposed areas.
Experience shows that the danger is generally greater on rock than on snow or ice, particularly in the presence of St. Elmo’s fire—silent electrical discharges occurring in highly charged air.
St. Elmo’s fire appears as bluish flames on sharp metallic objects such as summit crosses, poles, or antennas, sometimes accompanied by crackling sounds.
This phenomenon is an unmistakable sign of imminent danger.
It is also important to note that lightning often strikes repeatedly in the same area.
Warning signs not to be ignored
The risk of lightning may be preceded by clear warning signs:
- tingling sensations on exposed skin
- itching of the scalp and hair standing on end
- buzzing or vibration of metal objects
- appearance of bluish flames (St. Elmo’s fire) on exposed metallic points
When these signs appear, the thunderstorm is already upon you.
How to behave during thunderstorms and lightning
When a thunderstorm can no longer be avoided, it is essential to reduce the risk:
- avoid summits, ridges, spires, and dominant points, keeping at least 15 meters away.
- stay away from sharp rock features, isolated trees, cliffs, and vertical walls.
- place metal equipment (crampons, ice axe, carabiners, pitons) at a distance.
- avoid gullies, cracks, chimneys, caves, and large isolated boulders
- move away as quickly as possible from via ferratas and metal cables.
- avoid groups of people or animals
During climbing or rappelling:
- set up multiple anchor points.
- always use an autoblock knot while rappelling.
In the presence of lightning, snowfields and glaciers are generally safer than rocky terrain, provided you stay away from exposed high points. If no adequate shelter is available, adopt a crouched position, with feet together and knees drawn in, minimizing ground contact.
A fundamental concept
- Sheltering under a rock does not guarantee safety: electrical current can propagate through the rock and still cause injury. A lightning strike can reach temperatures of 30,000 °C and speeds of around 10,000 km/s.
- Against phenomena of such power, the only real protection is not being in the wrong place at the wrong time.
Advice from a mountain guide
In the mountains, when it comes to thunderstorms and lightning, there is no such thing as a 100% safe solution once the storm is already underway.
The only true defense is prevention.
In my experience, the most serious accidents do not happen because of lack of strength or technical ability, but because of poor time management: starting too late, ignoring warning signs, or insisting on “finishing at all costs”.
The advice is simple, even if it is often hard to accept: when the sky clearly shows danger, it is time to turn back. Turning around is not a failure, but a responsible decision. The mountains will still be there tomorrow.
FAQ – Thunderstorms and lightning in the mountains
Thunderstorms in the mountains can become extremely dangerous in a short time. The main risks are lightning strikes, strong winds, heavy rain, and sudden drops in temperature, especially on exposed ridges and rocky terrain.
Counting the seconds between lightning and thunder is a simple method: 3 seconds correspond to about 1 km. Other warning signs include buzzing metal objects, tingling skin, and the appearance of St. Elmo’s fire.
There is no completely safe shelter during a thunderstorm in the mountains. It is essential to avoid summits, ridges, isolated trees, and metal structures. Sheltering under rocks does not guarantee protection.
Experience shows that the risk is generally higher on rock than on snow or ice. In lightning conditions, snowfields and glaciers may be relatively safer than rocky terrain, provided exposed points are avoided.