Hello folks. I see a lot of misconceptions about hiking and thunderstorms so I wanted to add a blog to clear up some of these misconceptions. My name is Lars and besides being a hiker fanatic, I've always had an unhealthy fascination with thunderstorms. I have a masters degree in Meteorology and have been around forecasters for years. So I know a thing or two about forecasting and hiking with thunderstorms, which I would like to share with you. Of course you're welcome to disagree with anything I say, since to many of you I'm just a guy on the internet.
One of the mistakes that I see the most people make, is to download a random weather app on their phone and treat the output as gospel. Chances are that you've done a similar thing at some point. This in general is already a bad idea, but especially when it comes to thunderstorms, this is probably the biggest mistake to make. Why? Because thunderstorms are notoriously difficult to forecast, especially the location where they pop up. So while your app may display a sunny day for the location you typed in, it doesn't tell you that it predicts a thunderstorm 30 km away. The actual thunderstorm location can easily shift to your location, resulting in an unpleasant surprise. Especially when hiking, this could lead to dangerous situations.
So if the weather apps are unreliable when it comes to thunderstorms, what to use instead? Well lets first say that not all apps are bad. Some apps have a thunderstorm chance indicator, which is already a lot better than nothing. But these are also not flawless. A chance is a chance, and difficult to interpret. Better yet, is to take a weather forecast that has been written by a professional meteorologist. Their experience and knowledge of the local thunderstorm climatology is invaluable and can really help in making a much more accurate prediction. But most importantly, meteorologist are able to accurately convey the uncertainty that always accompanies thunderstorm forecasting, in a way that no weather app can. The downside is that these forecasts are almost exclusively in German, at least when it comes to the Bavarian and Austrian alps. But I really wouldn't recommend doing this unless I really thought it makes a much better prediction. Even if you know a little bit of German, you can already decipher quite a lot of information. You can also use google translate, but be prepared that the sentences will be a little bit juggled up.
Ok, so you say that is nice and all, but where do I find these forecasts from meteorologists and how do I read them?
There are in general 3 things that I want to know when hiking with thunderstorm risk:
- What time will thunderstorm formation start? Typically thunderstorms start to form in the early afternoon, and get stronger the later it gets. 14:00 is a typical time, but it can be a few hours earlier or later, depending on the circumstances.
- How many thunderstorms are expected? Will there be only a few or a lot? This is important, because the more thunderstorms are forecasted, the higher the chance I will get caught in one at some point. Sometimes forecasts identify specific areas with increased coverage of thunderstorms.
- How strong will the thunderstorms be? Thunderstorms come in all different sizes and strengths. Getting caught in a light rain shower is not nearly as bad as getting caught in a massive thunderstorms with large hailstones, heavy rain and hurricane force winds.
You are maybe wondering why I don't ask the question: "At what time can I expect a thunderstorm at my location?" This seems to be the question that weather apps are eager to answer, but the unfortunate thing is that you cannot give a reliable answer to this question. There is simply too much uncertainty in the prediction of thunderstorms.
Let's get back to reading forecasts. We start with an example: I want to go hiking tomorrow (Sunday 3 June) in the Bavarian Alps and I want to know what the thunderstorm risk will be. One of my preferred forecasts is the one that can be found on the website from our friends at the Deutsche Alpenverein. I'll navigate to the correct page (click bavarian alps and click the right date) and find the text below:
Bergwetter Bayerische Alpen am Sonntag, 03.06.2018
Der Sonntag beginnt mit viel Sonnenschein und geringer Bewölkung, oft ist es auch wolkenlos. Bis über Mittag herrschen stabile Verhältnisse und sehr gute Sichtbedingungen in den Bergen vor. Mit der kräftigen Sonneneinstrahlung entstehen im Tagesverlauf einige Quellwolken, die dann für lokale Sichteinschränkungen am Nachmittag sorgen können. Lokale, kurze Regenschauer sind zwar möglich, meist geht es aber trocken durch den Tag. Am Abend fällt die Quellbewölkung rasch zusammen, es folgt eine gering bewölkte, trockene Nacht. Die Temperaturen liegen in 1500 m zwischen 6 und 18 Grad, in 2500 m zwischen 2 und 10 Grad. Der Wind kommt in freien Kammlagen in 2500 m mehrheitlich aus Sektor Südwest mit 5 km/h im Mittel.
Now there is some important information to digest from this short forecast. I'll focus on the parts that are relevant for thunderstorms. "Bis über Mittag herrschen stabile Verhältnisse" means that the forecaster doesn't expect any storms before the early afternoon hours. This is important, because now you know that if your hike finishes before this time, you are almost 100% certain not to run into any storm. Lokale, kurze Regenschauer sind zwar möglich, meist geht es aber trocken durch den Tag. This is the most important line in the forecast. First of all the forecaster doesn't say anything about thunder, he or she only talks about rain. That already is an indication that thunderstorms are unlikely, and at most rainshowers are expected. But he also mentions that most places will not see any rain, indicating that only a few storms are expected. Concluding this forecast, I know that I can do a hike tomorrow without much risk. Not only do the storms not occur until after early afternoon, but they will not be numerous and not very strong, so the chances of me getting caught in one is very low. It cannot be ruled out completely though, so I will take a rain jacket with me just in case.
See below for a few more links with forecasts from different agencies for Bavarian and Austrian Alps. Remember that locations can be exchanged. In most cases a weather forecast for Tyrol also applies to the Bavarian Alps and vice versa.
Try to challenge yourself to make a forecast for tomorrow or the day after, with the text from the links above, using the three questions that I posted earlier. In this way you can accurately predict how high the thunderstorm risk is on a given day.
Hiking with thunderstorm risk
So we have established how to accurately establish the thunderstorm risk from a forecast. But what if we still want to do a hike despite the risk? Well this is quite a reasonable request. Thunderstorm risk happens almost every day during the summer months. Calling off all hike plans when there is even a slight risk of thunderstorms means you will not be hiking for most of the summer. So how do we minimize the risk for ourselves when there is a risk of thunderstorms? Here are some tips that I adhere to:
- Probably the biggest things you can do to reduce your chances of getting caught in a thunderstorm is to start and end the hike as early as possible! Skitourers are familiar with this rule for avalanches, but it goes the same for thunderstorms. Almost all thunderstorms occur in the afternoon, and get stronger the later in the afternoon it gets, so finishing the hike as early as possible is the best way to make sure that you don't get an unexpected visit by a thunderstorm. If you finish at 15:00 instead of 17:00 you are already reducing your chances significantly. But earlier is even better.
- Don't be at the peak when the thunderstorm starts. This tip connects to the previous point of starting early. Make sure to do the peak early in the day, don't linger too long and descend fast afterwards. Don't think that you can wait until you hear or see the thunderstorm before descending: Thunderstorms are much faster than you. The most dangerous place to be during a thunderstorm is at the peak. The second most dangerous place is on an exposed ridge. In general: the lower you are the safer you are. Not only does it reduce the chances of a lightning strike, but the lower trails are much better to traverse during heavy rain that accompanies thunderstorms.
- Always have a backup plan. If there is a risk of thunderstorms, check the map the day before and see if there is any alternative route you can take. Any trail that gets you to lower altitude fast is good. Don't be afraid to turn around and backtrack if needed. Set yourself an ultimatum: "If I see or hear a thunderstorm before point X, we will take the alternative route".
- Always take a rain jacket if there is even a slight chance of thunderstorms. An extra warm layer helps too. Thunderstorms produce a lot of cold air. Even in the summer the temperature can plummet during a thunderstorm and depending on the altitude you could be at risk of hypothermia. Keeping yourself warm and dry during a thunderstorm is important!
- If you do get caught out by a thunderstorm, seek shelter if possible! If there are huts nearby, you are lucky! Cave? great, but stay away from the entrance, and be careful not to touch any floor that is wet. If these are not present, then it depends on the environment. In a forest? Keep walking. The trees are a much bigger target than you. You can't do anything to reduce your chances of getting struck. If lightning gets close, stand as far from any tree as possible with your feet next to eachother. In shrubs? Make yourself smaller and keep walking. Remember that getting to lower altitude is still important, but more important is not to slip and injure yourself on the wet trail. Out in the open? I don't need to tell you that this is the most dangerous place to be in during a storm. Make yourself as small as possible, reduce your surface by putting your feet together and pray to whichever god(s) you believe in. Remember that you are only a small speck of dust on the mountainside, and your chances of getting struck are still very low. Stay away from anything that makes you a bigger target, like a single tree, a metal fence or a steel cable. You don't need to touch it to get struck: Lightning can travel though the ground and still strike you, but distance matters! The further you are away from these objects, the better. Contrary to popular belief: you don't have to throw away anything metal. Lightning doesn't care. It only cares about your size.
In the end the risk is still there, even though we try to minimize it. After taking all the precautions there is still a risk that you can get injured or worse during a storm. Does that mean we should not go into the mountains when thunderstorms are forecasted? Well that is up to everyone to decide. Some people like to take more risk than others. Personally I believe that since there is never a day without risk in the mountains, even without thunderstorms, some risks are acceptable. But don't make the risk bigger than it needs to be.