Thunderstorm chaos in Bern: 8,500 lightning strikes, squalls and risk of flooding!

Thunderstorm chaos in Bern: 8,500 lightning strikes, squalls and risk of flooding!

On June 5, 2025, Switzerland was again affected by intense thunderstorms, which led to a significant increase in lightning activity. Over 8,500 lightning strikes were measured, of which more than 2,000 were registered in the canton of Bern. These numbers show that despite the intense lightning activity compared to the summer of 2024, when over 50,000 lightning strikes were counted in a single day, the current thunderstorms still represent a significant force of nature.

The thunderstorms brought not only lightning and thunder, but also extreme weather conditions. At low altitudes, the thunderstorms caused strong winds, which blew at speeds of 86 km/h in Courtelary and even up to 90 km/h in Altdorf (due to foehn-like squalls). In addition, rapid rain was reported in the north of the country, while the upper Maggia and Verzasca valleys suffered from prolonged rain, reaching over 100 liters per square meter. Such extreme rainfall attracted the attention of emergency services, especially in the upper Basel area, who had around 70 missions due to flooding and overflowing streams.

Necessary measures

The fire brigade was in great demand, particularly when it came to pumping out flooded basements in residential buildings. Train cancellations and restrictions on the railway line between laufenlfingen and Sissach were also a result of the storm damage. In Graubünden, the cantonal road in Misox was closed for safety reasons due to heavy rainfall. This closure specifically affected the evacuated part of the southern Grisons village due to the acute risk of landslides.

Special attention was also paid to the lightning technology aspects. According to information from LightningMaps.org, a “stroke” is a single lightning event that is detected by lightning tracking networks. Lightning locations are visualized on maps, enabling detailed analysis of lightning activity. These visualizations are critical to better understand and predict the dangers posed by thunderstorms.

Different terms are used in communication about lightning. A "flash" describes multiple strokes that occur almost simultaneously in a small area, while the term "strike" usually describes a lightning bolt that strikes from the sky to the earth. Despite the technical challenges and the necessary precise data processing, lightning data is essential for safety precautions during thunderstorms.

The weather conditions of the last few days reinforce the importance of well-organized emergency management and the continuous improvement of forecast systems in order to provide the population with timely, helpful information. Switzerland has once again shown that extreme weather events represent a constant challenge that requires both technical and human resources to overcome.