Severe thunderstorms with six-centimetre hail hit northern Switzerland

Violent weather front crosses northern cantons

A sharp cold front collided with hot, humid air on Friday morning, unleashing severe thunderstorms across western, northwestern, and northeastern Switzerland. The weather service SRF Meteo recorded approximately 46,000 lightning strikes within a short window as storm cells tracked along the Jura mountains toward Lake Constance. Two distinct hail corridors developed, stretching eastward from the Basel region and Lake Neuchatel. Wind gusts reached 142 kilometres per hour in Canton Schaffhausen, bringing down trees and scattering debris across roads. Meteorologists noted that the system displaced an unusual late-August Fohn setup, following an overnight period where temperatures in Fohn valleys remained above 25 degrees Celsius and reached 29 degrees in Vaduz.

Record hail sizes and intense short-term precipitation

Hailstones reached diameters of up to six centimetres in the hardest-hit corridors between the Seeland region, Canton Aargau, Zurich Unterland, and Lake Constance. Meteorologist Peter Wick explained that powerful vertical updrafts suspended ice particles inside the cloud layer, allowing them to accumulate successive coats of supercooled water droplets before falling. Wick noted that hail of five centimetres or more remains unusual in Switzerland and described the formations as rare colossuses.

Above all, it requires a very unstable atmosphere, sufficient moisture and strong vertical air movements.

The storm also delivered localized downpours that met the official threshold for heavy rain within minutes. Hallau in Canton Schaffhausen registered 23 millimetres of rainfall in ten minutes, while Langenbruck in Canton Basel-Landschaft recorded 19 millimetres and Barmelweid in Canton Aargau recorded 18 millimetres.

Transport disruptions and widespread structural damage

The severe weather brought substantial disruptions to the Swiss transport network and public infrastructure on Friday morning. The Swiss Federal Railways (SBB) suspended train services on the route between Biel and Olten, with the outage expected to last until roughly 14:00. Operations on the regional R55 line near Nyon in Canton Vaud were also affected by storm damage. On the A1 motorway near the Birrfeld junction in Canton Aargau, strong winds caused a truck to tip onto an adjacent delivery van, though no injuries were reported. Additional vehicle incidents occurred on the A1 near the Baden exit and along the A51, where drivers faced broken windscreens and slippery road surfaces caused by stripped foliage.

Emergency services mobilize in Solothurn and Aargau

Cantonal authorities and utility companies handled hundreds of emergency calls throughout the morning as property damage reports mounted. In Canton Solothurn, the cantonal police logged well over 200 damage incidents before midday, primarily involving shattered windows, stripped roof tiles, and crushed vehicle glass. In Canton Aargau, emergency crews responded to four collapsed power poles in the Birrfeld area, including one pole that fell onto a residential building. Local energy supplier AEW Energie AG reported electricity interruptions across several municipalities in the Fricktal district. Bernhard Graser of the Aargau cantonal police noted that emergency lines received storm-related reports every minute as the front passed through. In Aarau, winds ripped off sections of a sports hall roof, while collapsed tents and scaffolding destroyed the grounds of a planned festival at Kantonsschule Wettingen. Police confirmed no initial reports of injuries from the morning storm.