You’re on holiday in the Alps and planning a hike in the mountains, you’re well prepared – your rucksack is packed and you’ve got food, clothes, walking poles, a map and GPS…
But even if you’ve checked the weather and everything looks good, the weather in the mountains can be unpredictable and there is a chance of stormy weather.
Is a mountain storm dangerous? What should you do to keep yourself safe? Here are some useful tips …
Check the weather forecast before you set out
Plan your exit
In the event of a storm in the mountains, it’s good to have a plan in place! Check websites that will give you precise information on the local weather situation over the coming hours. The MétéoFrance website has a useful mountain weather tab.
Dangerous thunderstorms are often predicted on the Keraunos website, run by the French Observatory of Tornadoes and violent storms.
Météorage is said to be a world specialist site for lightning detection. It won an award in 2019 for its contribution to protecting people in hazardous weather and can alert you in the case of a storm.
Check the weather regularly before you head out, and again during your hike. This will make it easier for you to alter your route or seek shelter if necessary. IGN maps can help you find paths, huts or alternative routes – you can install the IGN apps on your phone.
Postpone or cancel your trip
If a storm is on its way, it’s best to be cautious and not take any unnecessary risks. The best advice is to avoid the mountains if there is any doubt about the weather and consider cancelling or postponing your trip for a day or two.
Please note: one in three victims of lightning strikes does not survive, and those who do may suffer serious after-effects. Lightning can transmit current through the ground near an impact. If you suspect you have been affected by lightning, it’s wise to consult a doctor.
How can you tell if a storm is on its way?
Storms can develop very quickly in the mountains, so any sign of lightning or thunder should be seen as a warning, even if it seems far away. Check the warning map on the MétéoFrance website to see if a storm is on its way.
Generally speaking, there are several signs to look out for, but these are different depending on the kind of storm:
- Look at the clouds: Cumulus clouds, isolated dense clouds with clearly defined edges, can change into castellanus clouds – partial swelling and with a crenellated appearance – then into cumulonimbus storm clouds, often in the shape of an anvil. Cumulonimbus clouds are a good indication of a thunderstorm and can be of an impressive size. Click here to understand how a thunderstorm forms.
- The sky gets dark very quickly, and sometimes black if the storm is particularly violent.
- The wind gets stronger and becomes gusty.
- Temperatures drop.
- Heavy rainfall may occur.
In the mountains, there are often signs that lightning is imminent. The air starts to vibrate, and you may hear buzzing sounds. You might also feel as if your hair is standing on end.
What are the dangers of a mountain storm?
Thunderstorms can always pose dangerous risks. Here are the main dangers:
Lightning
This is the most dangerous aspect of a thunderstorm. This high-intensity electrical discharge can be fatal for humans and animals and can also start fires.
Strong winds
The wind blows strongly under a cumulonimbus cloud – often up to 140km/h. It can also change direction all the time. More rarely, a wind vortex can form, causing a devastating tornado.
Hail or rain
The intense rainfall that often accompanies a thunderstorm can cause rivers to burst their banks and give rise to devastating floods.
During a thunderstorm, between 50-100 litres of water can fall per square metre in just a few hours. Rain can also cause rocks to become unstable and temperatures to fall.
Hail, a form of solid precipitation, can destroy an orchard or vineyard in record time. Plus, hailstones falling on your head can be very painful.
How to react in the event of a mountain storm
Don’t run
If you’re caught in a storm, don’t run. The best thing to do if lightning strikes the ground near you is to stand still with your feet together which can greatly reduce the impact of ground lightning.
Insulate yourself from the ground
The best position to avoid being hit by lightning is to crouch with your feet together and your arms around your knees. If possible, stand on an insulating layer, such as a sleeping bag or a ground sheet.
Don’t huddle in a group
Move several metres apart to avoid chain lightning and the transmission of electric current in a sideways flash.
Stay away from metal objects
Make sure you stay away from your ice axes, walking poles, crampons, carabiners, pitons etc. Avoid any metal structures such as fences or pylons. You should also keep away from your mobile phone.
Avoid high-risk places
Places considered high risk include:
- Forests: because the wind could cause branches to fall.
- Isolated trees: because lightning is attracted to the highest point in a meadow or clearing.
- Ridges and summits: these are possible points of impact and therefore vulnerable to lightning strikes. In the mountains, move away from ridges and peaks at the first signs of a storm. Try to get to lower ground as quickly as possible (at least 30m below a ridge or summit) and find shelter on a ledge.
- Walls: never lean against a wall. It’s best to keep at least 1.5m away from a vertical rock, the bottom of a cave or its ceiling. Lightning and torrential rain can cause rockslides.
- Precipices and ravines: You’re more likely to fall in a storm, due to the wind and fear, so avoid these dangerous areas.
- Water: in a storm, you should stay away from any area of water that could conduct electricity, such as lakes, rivers or streams.
Where should you shelter in a mountain storm?
- The valley floor will be less exposed to the storm. Avoid staying on the mountain and try to get as low as possible.
- Mountain refuges and churches are safe shelters and sometimes have lightning rods. However, if in doubt, stay away from the walls of the hut, as they can conduct electricity.
- Caves can protect you from rain and falling rocks. Stand as far from the entrance as possible and do not touch the walls or ceiling.
- Your car: if you are near the car park, sit in your car with the windows and doors closed. The metal body and chassis of a car can deflect the lightning towards the ground, keeping you protected.
Useful equipment in a mountain storm
Make sure you put the following items in your rucksack:
- Waterproof clothing (a rain jacket or poncho) to keep you dry in the rain.
- A change of warm dry clothes – the temperature can drop significantly in a storm, so warm clothes will stop you from getting cold while you wait for the storm to pass.
- Some material that can insulate you from the ground that you can crouch on while waiting for the storm to pass (eg a groundsheet or sleeping bag).
Lightning and other elements triggered by the storm (overflowing rivers, falling branches, landslides etc) can be fatal. However, if you are caught in a storm, you now have some advice that will help you stay safe.
Make sure you subscribe to our newsletter so that you are informed when we publish new articles, and for more information on walking in the mountains, check out these articles.
- What to do if you meet a Patou sheepdog in the mountains
- Which animals can be found in the mountains in spring?
- La Clusaz hiking: the top trails for all abilities
- The best hiking routes in Chamonix
- The best walks in the Alps
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