Principle of the shock wave

Every five seconds, the cannon fires ionizing (energy-rich) shock waves into the air. These quickly reach the higher atmosphere, up to 10,000 m, at -50°C, where the hails forms.
Part of the waves is being bounced back by the clouds and the tropopause. These collide with the climbing waves.

Hereby their speed and energy increase and they carry a large ionizing potential (ionizing is the process of knocking away electrons).
By the continuous up and down movement of the waves, a mix of polarities is created inside the cloud. This leads to a chain reaction of micro explosions which makes the ice crystals unstable.

They cannot absorb water drops or vapor anymore. They fall down and during their fall they cross the disturbance zone that is caused by the shock waves. Hereby the stones are fragmented.
The hail finally reaches the ground as rain or wet snow.