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I just got back from a guided walking trip to high mountains. There was one day when we encountered a thunderstorm - and the guide advised we are OK to proceed with the day's walking, instead of turning round. He gave an explanation, and I wonder if you think it is reasonable?

The situation was as follows: the forecast said 'possibility of thunderstorms', for just-about all the foreseeable future. We set off from our overnight stay up the valley, heading for a high mountain pass. We then heard the thunderstorm coming, staying about 1.5-3 km (1-2 miles) away from us, as deduced from timing between lightning and thunder.

Now, the guide said he is happy to proceed up the valley and up to the col, because

he was monitoring the pressure (with a gauge in his GPS), and it was stable - indicating that the storm was going remain where it was, and not migrate / descend towards us.

Does that make sense?

More generally, the advice I have been given was that if you hear a thunderstorm, you unconditionally turn around and seek solid shelter (mountain hut etc.). Is that too conservative, and if so, what are the mitigating circumstances? I understand you are never 100% safe from lightning outside solid buildings.

  • You're not safe in a building, either. Lighting can go right through. – Don Branson Jul 31 '16 at 21:46
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    I suspect that the guide was relying on his knowledge of the behavior of storms in that area, but rather than simply saying "Trust me" came up with "monitoring the pressure" because it sounded scientific. Note that you were walking uphill, so the pressure was going down anyway; how he could separate the two effects.....maybe, but I am suspicious. I'd like to hear from someone who really knows. – ab2 Jul 31 '16 at 23:27
  • @ab2 If you correlate the pressue change with your GPS height you can separate altitude induced from weather induced pressure changes – at least to a certain amount, but with good approximation if your direction of elevation change is constant and you have can monitor it over some time. – Benedikt Bauer Aug 1 '16 at 17:30
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    @Benedikt Bauer I'm still from Missouri on this one (idiom for doubting). If the thunderstorm heads your way, what is likely to be the pressure drop (expressed in apparent altitude) and how much time between the pressure drop and when the storm hits you? Yes, you can do the subtraction between real altitude gained and apparent altitude gained in your head while herding a group of tourists, but keeping an eye on the sky seems just as good to me. – ab2 Aug 1 '16 at 18:52
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In general the idea (#1) of the guide is not a bad one but it is way simplifying weather forecast. It is not as easy to predict even short-time. Of course it could be a local guide with lots of experience (we don't know that by your question and maybe you also didn't know while on tour) and he will be right most of the times because he knows his mountains well.

Still, high intensity weather conditions like arising storm aren't stable and easy to forecast. Things like moving direction and intensity can change quite rapidly. So this conservative idea #2 to search shelter in possible danger of lightning strike is a better idea than #1 in my opinion.

What's most important here and missing in the question: What type of tour was it and on what kind of mountain? E.g if you are happily scrambling a via ferrata on an exposed mountain, I - without thinking a second - search ways to get shelter or off the route IMMEDIATELY when the first signs of lightning storm show up. Other extreme, walking through dense forest on the way to the approach hut while lightning might not be that bad (depends on winds but you are more secured to lightning strike). I guess you get the idea, conditions also count a lot for this kind of question.

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    Thanks. For context, it was all high above the tree line. That said, there were plenty of much higher things around us (peaks and ridges), just not immediately close to us. – Bennet Aug 1 '16 at 21:28
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The guide's argument seems to be reasonable. However, I would not recommend to simply copy that behaviour but try to go with the more conservative advice you were given.

The guide has one big advantage compared to you: He is roaming this area all the time – if he is a local guide, if not he has at least lots of experience with mountainous areas in general – so he knows very well about local weather phenomena (see also Do Mountains really make their own weather and if so why?). With this knowledge monitoring the air pressure can be a good means to see whether it is still safe to go or if turning back is better.

However, as already said, I would not recommend to do so yourself and stick to a more conservative approach instead.

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