A thunderstorm in the mountains can be really impressive: the rain pours down in torrents, gusts sweep over the mountain tops, lightning cuts through the cloud cover brightly and powerfully and thunder roars through the valleys – all this is unproblematic when peering out of the windows of a cozy mountain hut.
Stupid only if you are on the wrong side of the window pane – then it quickly becomes dangerous, even life-threatening. Because such lightning bolts can be several 100,000 amperes strong. And in addition to the direct impact of lightning – i.e. lightning hitting people directly – there is also the indirect impact, namely: lightning hits a tree and is transmitted from there through the ground. This is why the first and foremost rule for all-mountain lovers is the following: Do not get caught in a thunderstorm!
Plan & Get Informed
The good news is that day to day general weather reports are already very accurate. The bad news: Thunderstorms are often so small-scale that even a mountain weather report cannot predict them correctly. So it’s up to you to keep your wits around you.
Nevertheless, the weather forecast forms the basis of all planning: If it predicts the likelihood of thunderstorms, it is necessary to calculate accordingly: Since many thunderstorms are caused by the sun’s rays during the day, storms often do not form until midday or afternoon. That’s why you should start your tour as early as possible in the day – and be back in the valley long before the critical phase. On long tours, “early” sometimes means: when it’s still dark! If this is not possible, the route should be chosen accordingly: shorter tours with a quick descent into the valley are the measure of all things here.
- Tip: You can find a weather report specially tailored to the weather in the mountains, for example, at the German Alpine Club. Click here for the German alpine club’s mountain weather service.
If the air is cool and fresh in the morning, this is a good sign, but if it is already warm and humid in the morning, thunderstorms are more likely.
However, weather reports and cool air are only clues; what is important is a regular and critical look at the sky. There you look for the so-called cumulonimbus clouds. You can recognise them relatively easily, as they extend far upwards and form small clusters at the top, reminiscent of a cauliflower. On the underside they are mostly flat. It becomes critical when, over time, the cloud piles up further and further upwards until it reaches a barrier layer where it spreads out horizontally. This creates the shape of an anvil. The nasty thing about mountains: you don’t always have a view to all sides, often walls or peaks block the view in various directions.
The barometer of a GPS watch can also announce a thunderstorm, but not always. There are cold front thunderstorms and warm front thunderstorms. In a heat storm, intensive solar radiation causes moist warm air to rise to high altitudes. In a cold front thunderstorm, moist warm air meets a cold front. The approach of this cold air front can be seen by a rapid drop in the values on the barometer. Furthermore, this cold front is often mentioned in the weather forecast. The problem is that it is the heat storms in particular that often strike in summer, and they strike quickly and in an extremely regionally limited fashion.
So what do you do if you are surprised by a storm in the mountains? Here are a few important tips for the most common mountain sports:
How do I behave when hiking and climbing?
The first rule is: get to safety. Don’t waste time with any counting exercises, how much time lies between lightning and thunder, if you hear thunder, you have to act, full stop. Rather, use your mental capacities to leave exposed areas, i.e. peaks, ridges, and the like, quickly and with concentration. Try not to be the highest point of your surroundings. You should also avoid isolated trees, groups of trees, and forest edges. By the way, lightning doesn’t care which wood it strikes. Beech, birch, oak – it takes it all. If you are fast enough, you can descend into the valley or to the next hut. If this doesn’t work, you should find a safe place. When walking, keep your distance from walls and wet (wire) ropes – and remember that not only is lightning dangerous, but you could also fall or injure yourself in other ways. So keep control when you retreat!
Even if it is not yet completely clear how lightning “searches” its targets, one thing is certain: metal should not be worn on the body. This applies to skis and axes, but also to hiking poles. They can all announce a close lightning strike when they start to vibrate. In this case, throw them quickly a few meters away from you. You should also take off crampons for the duration of the thunderstorm. However, please remember that crampons and axes are important for safety, so find a place where you don’t need them at the moment to stand or walk safely.
How do I behave when on a via ferrata?
Congratulations, you’ve hit the jackpot: your via ferrata set is suspended in one of the world’s largest lightning rods. The first and most important measure is, therefore: stay of the wire. There are often passages in via Ferrata where you can cross out, there are niches, emergency descents and walking terrain. Don’t just think of the options above you, but also below you. Maybe there was a recent via ferrata passage to which you can descend again? Get yourself there and sit as far away from the cable as possible – at least one metre, better three metres. Of course, you have to tie yourself down. So make sure you are self-securing, a mini ledge over a precipice that is only half a metre away from the rope can also prove to be a trap. Until you are in a halfway safe place, you have to keep your foot on the gas! And the next time you think about it: via Ferrata are not a good idea if there is a tendency to thunderstorms. You can read about how to behave in a safe place below.
What can I do when alpine climbing?
Alpine climbing is just as problematic in a thunderstorm as via ferrata climbing – perhaps even a little more dangerous: a lightning strike at the top can spread over large parts of the wall, cause rockfall and also spread via the (wet) climbing rope. And there are hardly any rest areas that are not exposed. Certainly, the best option is to rappel early. Also, remember that a wet wall is much more difficult to climb after a thunderstorm. That is why abseiling will be the method of choice anyway in most cases. If this does not succeed in time, you might be able to crouch down on a ledge somewhere (see below for instructions), wait and hope.
What should I consider when mountain biking?
Although the tyres of your bike are made of rubber, you ride around with a huge metal box under your bottom – no, a mountain bike is not a Faraday cage and therefore you are not protected against lightning on the bike. In the case of thunderstorms, interrupt your ride and keep at least three metres distance from the bike.
What is a safe place and how do you behave there?
The safest places are mountain huts, sheds or bivouac boxes with lightning conductors. If the accommodation does not have a lightning rod, you should keep at least one metre away from the walls and ceiling. If there is no man-made dwelling available, caves, places under ledges or at the foot of walls can also offer some protection from lightning – although perhaps not from falling rocks.
Although individual trees are rather a bad idea, the interior of a forest with a uniformly high tree population offers a slightly lower risk. A distance of at least ten metres to all trees and branches is optimal. Think about wind breakage: thunderstorms can bring a fair amount of wind and shake dead branches from their crowns or uproot trees. In open spaces you should try not to be the highest point, hollows or depressions are a good idea.
Not only direct hits are dangerous. Lightning that strikes somewhere else and spreads from there and hits you can also be life-threatening. To avoid being part of such a transmission, you should not stand in water or in the wet (keyword muddy meadow) and keep at least one, but better three metres distance to each side of rock faces and to other people.
And since lightning does not only spread over long distances but can also hurl people a few metres away, you should, of course, keep the danger of falling in mind, especially if your resting place is near an edge or could be at risk of falling rocks. If lightning and thunder are less than ten seconds apart, there is an absolute danger to life. At this point at the latest, you should stop walking and take up a safe position: Stand on your backpack (and/or on a rope), this offers a little more protection and takes you away from the damp ground. Put your feet close together, crouch down and wrap your arms tightly around your knees – make yourself as small and compact as possible. Not only because of your size in the terrain but also to keep your stride tension as low as possible.
There is no danger if you have not heard thunder for at least 30 minutes.
Tip: Always keep a cool head
Storms are bad, yes, and the threat of lightning is real. And, of course, people die again and again from the force of nature or suffer terrible injuries. However, thunderstorms are frightening, and it can happen very quickly that people act headlessly because of the violence above their heads. Anyone who acts too hastily and unfocused or moves too fast in difficult terrain will also put himself and the group in a dangerous situation. This can happen through a simple twisting of the rope, through which you can no longer or only very slowly make progress and perhaps even need to be supported. But it can also lead to a (crash) fall. The probability increases when rain makes the paths and rocks more slippery.
So here’s a tip: calculate well, plan checkpoints and alternatives, turn back in time and – if there is no other way – rather hold out for the storm in an uncomfortable but reasonably safe position. A lightning strike is not automatically a death sentence – but a deep fall on a ridge often is.