Hailstorms are exceedingly common in Switzerland and not limited to certain geographical areas. Any damage is determined by the grain size and density of the ice. Rare events with grain sizes of over 3 cm usually cause major damage not only to agricultural crops, but also to cars and buildings. Very large grains can also pose a direct risk to people and animals.


Hail does not occur without a thunderstorm. Conversely, there are many thunderstorms without hail. Either because the atmospheric conditions are not suitable for hail to form, or because the hail or sleet grains are so small that they melt when they fall and only reach the ground in the form of torrential rain.

As a rough rule of thumb, hail appears about every tenth thunderstorm. The danger of hail is greatest in areas where cold, dry air masses meet warm, humid air masses and in mountainous regions where mountain masses further increase convection.

Thunderstorms are caused by sudden, acute vertical shifts in the atmosphere. They develop either when the sun shines intensely over hot land masses or when different air masses collide, especially when summer heat waves are broken by a cold front advancing over a large area. For this to be possible, the atmospheric layers must be unstable.

The updraft inside the thundercloud must be sufficiently high to produce large hailstones. If the grains are kept suspended, they can extract the water droplets and ice crystals from the cloud air flowing around them and continue to increase in size.

The updrafts are usually concentrated in narrow funnels within the thunderstorm. If the uplift in an updraft funnel suddenly weakens, the previously suspended droplets and mass of hailstones suddenly fall to the ground.

One and the same thunderstorm can trigger several hailstorms which are spaced apart from each other. Usually, a hail strike, or hail swath, as the continuous hail area is called, is a few kilometres long and less than one kilometre wide.

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