Around the world, lightning strikes are much more frequent in the mountains than in the lowlands. Thunderstorms are undoubtedly one of the most dangerous phenomena for mountain tourists. In the Tars, the storm season usually starts as early as April. But the actual thunderstorm season lasts from May to August, with the highest number of thunderstorm days recorded in July for years. In September, storms in the Tatras are much less frequent and their frequency is similar to that in April. In October, sometimes one storm is recorded, in the remaining months storms are practically absent, and if they do occur, they are the result of weather anomalies.
Most thunderstorms in the Tatras, as in the rest of the world, occur in the afternoon. An equal number of storms occur in the evening and at night. However, it sometimes happens that thunderstorms even appear in the morning and before noon. This is usually associated with the passage of an atmospheric front accompanied by extended cumulonimbus.
During the thunderstorm season, it is essential to check the forecasts before going to the Tatras. Most storms are already visible in them the day before. To be safe, it is also worth checking on the trail whether the forecast has changed. And it is essential to observe the weather. Storms do not just appear out of nowhere. Clear signs that a storm is approaching are a lack of wind, a baking sun and heavy, muggy and cloudy air. Another is the appearance of buoyant clouds.
The process of convective thunderstorm formation, and such storms occur most often in summer, during periods of strong sunshine, is usually visible tens of minutes in advance. A cumulus congestus can change into a thunderstorm cumulonimbus even within a few minutes. But it is the frontal storms in Poland that are usually the most dynamic and the most violent. That is why summer hikes should start at dawn - so that you are already off the trail in the afternoon, when the risk of a storm increases.
Scientists can predict the occurrence of thunderstorms with a high degree of probability, but it is not possible to predict where lightning will strike. Unfortunately, it is also still impossible to know how strong a storm will be and how much lightning it will have. In recent years, scientists have also noticed a change in the type of discharge, probably linked to climate change. Multiple, hybrid discharges, which are stronger but less frequent, are now much more common. The current intensity contained in them reaches enormous values.
It is worth remembering that lightning can strike even within a few kilometres of a formed storm cloud and that it will move quickly. Therefore, when a storm finds us on the trail, it is important to assess how far away it is. We can do this thanks to the laws of physics. Simply count the seconds from flash to thunder. A 3-second difference means that lightning has struck a kilometre away from us. 5 seconds is 1.7 km and 10 seconds is 3.4 km. In the mountains, a thunderstorm as close as 30 km away should already alarm us (about 30 seconds from flash to thunder).
What to do when a storm is close and we are on the trail? If you are on a ridge or summit - get as low as possible as quickly as possible. Do not seek shelter under a lone tree or directly under a rock (keep a minimum distance of 1 metre from the rock), as such places may become a target for lightning. In the Tatras, when descending from a ridge, it is best to hide in a low stand of trees, such as dwarf pine. Places close to bodies of water, streams and even - alcoves should absolutely be avoided. Also, do not stop in terrain with artificial facilitations such as metal ladders or chains. Also, Tatra huts are not a protection against thunderstorms, as they do not have lightning conductors. If you are hiking in a group - you should not crowd in one place, but stand at parometre intervals. Then you should remove your backpack and switch off all electrical appliances.
During a thunderstorm in the field, it is advisable to crouch down with your feet close together and tilt your head. It is best to put a rucksack or a carrimat under your feet, which will give you extra insulation from the wet ground. It is safe to continue hiking only 30 minutes after the last thunder is heard.
In the history of TOPR, as many as 70 lightning fatalities have been recorded in the annals of accidents. Most in the Giewont area. On 15 August 1937, then, 4 people died on Giewont and 130 were injured. Exactly 2 years later, on 15 August 1939, lightning struck the summit of Świnica. Six people died and 15 were injured.
The most tragic storm in the Tatras, however, took place in the 21st century. Undoubtedly, the magnitude of this tragedy is linked to the exceptional popularity of mountain tourism in recent years. On 22 August 2019, 157 people were injured and 4 died as a result of the storm on Giewont and in the Red Peaks range. On the same day, 1 person died in the Slovak Tatras. The most casualties were caused by a lightning bolt that struck the summit of Giewont at around 13:25. A large number of people were in the vicinity of the summit, although thunder was heard half an hour before this strike.
Dozens of hikers failed to turn back from the trail. Many suffered paralysis as they clung to metal chains. The current also flowed over wet rocks. Some of the victims were thrown back by the force of the impact and suffered numerous injuries (including fractures and bruises) as a result of falling from a great height. Lightning strikes caused stones of various sizes to splinter, injuring more people. On the Polish side, about 180 rescuers were involved in the rescue operation, including 80 TOPR rescuers. The injured were evacuated from the Tatra Mountains for several hours by TOPR, LPR and Police helicopters. A total of 56 people were hospitalised.