A powerful and unusually long-lived thunderstorm swept across northern Switzerland on Friday, August 28, producing hailstones up to 6 cm (2.4 in) across parts of the country and leaving widespread damage in canton Aargau.
Aarau and surrounding communities were among the areas hit as the storm raced eastward across the Swiss Plateau during the morning, accompanied by torrential rain, violent wind gusts and intense hail.
Aargau Cantonal Police said the severe weather reached the canton shortly after 09:00 local time. Within hours, authorities had registered around 240 damage locations, while more than 40 fire brigades were deployed across the canton.
A violent storm swept across Switzerland, bringing near-black skies, torrential rain, powerful winds and damaging hail from the Bern region toward Aargau and Zürich.
— Strange Sounds (@Strange_Sounds) August 29, 2026
Some pretty wild scenes for Switzerland. 😳
🎥👇 pic.twitter.com/CgUBgXBc6M
Trees were uprooted, roofs and scaffolding were damaged, streets and basements flooded and vehicles were battered by hail.
In Aarau itself, parts of the roof of a sports hall were torn away during the storm.
Hailstones reached 6 cm
One of the most remarkable features of Friday’s outbreak was the size and geographic extent of the hail.
SRF Meteo reported hailstones reaching around 6 cm (2.4 in) in diameter in the strongest parts of the storm, comparable in size to a tennis ball.
The hailstorm left a long corridor of damage stretching from the Seeland region through Aargau and the Zürcher Unterland toward Lake Constance.
Heavy rainstorm with hail hits Aarau, Aargau, Switzerland 🇨🇭 (28.08.2026) pic.twitter.com/8PNIg9czjX
— Disaster News (@Top_Disaster) August 28, 2026
SRF meteorologist Simon Eschle described hail of this size as highly unusual. At any individual location in Switzerland, hailstones of this magnitude have an estimated recurrence interval of roughly 30 to 50 years.
Insurance companies were quickly confronted with thousands of claims.
Allianz Suisse said Aargau, Solothurn and Zürich were among the hardest-hit cantons and initially expected more than 10,000 claims following the storms, many involving hail-damaged vehicles and buildings. Special inspection centres were established, including one in Aarau.
Mobiliar separately described the outbreak as its most severe thunderstorm event of 2026 so far.
Power pylons toppled near Birrfeld
Some of the most dramatic wind damage occurred east of Aarau around Birrfeld and Birrhard.
Large concrete electricity pylons were toppled during the storm. Grid operator Axpo later reported damage to eight concrete pylons along the A1 near Birrhard.
One pylon fell onto a recreational hall and another struck a commercial building.
At around 09:50, violent winds also overturned a truck travelling on the A1 near Birrfeld. The truck fell onto a delivery van beside it, although neither driver was seriously injured.
Nearby Birrfeld airfield sustained damage to aircraft and hangars.
The storm also tore through infrastructure being prepared for the Argovia festival, flattening tents and barriers and damaging the roof of the stage.
Farther east, the same severe-weather corridor generated exceptionally strong winds. A gust of 142 km/h (88 mph) was measured at Schaffhausen.
Why did the storm become so powerful?
The outbreak developed ahead of an advancing cold front crossing Switzerland.
Warm and humid air was already present over the Swiss Plateau when cooler air began approaching from the west. The resulting temperature contrast helped destabilize the atmosphere, while the front provided the lifting mechanism needed to initiate deep thunderstorms.
Once established, the strongest storm remained organized for an unusually long period while moving northeastward across northern Switzerland.
Its powerful updrafts were capable of carrying developing hailstones repeatedly through regions of supercooled water high inside the cloud. Each journey allowed additional layers of ice to accumulate until the hailstones eventually became too heavy for the updraft to support.
That process allowed some stones to grow to around 6 cm.
At the opposite end of the storm circulation, intense downdrafts carried cold, dense air rapidly toward the surface. These bursts of descending air likely contributed to the destructive straight-line winds responsible for fallen trees, damaged structures and toppled pylons.
The atmosphere was also electrically explosive. Around 46,000 lightning strikes had been detected across Switzerland by late morning, with the total climbing to approximately 53,000 by 18:30.
The combination of very large hail, torrential rainfall and destructive winds made the August 28 outbreak one of Switzerland’s most significant thunderstorm episodes of the summer.
While the storm moved away rapidly, cleanup and damage assessments continued across Aargau and neighboring cantons.
The most striking aspect was not simply the intensity at one location, but the storm’s ability to remain organized while crossing a large portion of the Swiss Plateau, leaving a remarkably long corridor of severe weather from western Switzerland toward Lake Constance.
