In a storm cloud, water droplets are brought upwards in an updraft within the storm clouds. The droplets cool and freeze into hail and smaller ice particles as they rise upwards. The heavier hail particles that formed then fall back downwards, rubbing against the rising small ice particles.

Electrostatic charging by friction occurs, with the hail particles gaining electrons from the small ice particles. The heavier hail particles, which have become negatively charged, gathered at the bottom part of the storm clouds, while the lighter small ice particles, which have become positively charged, gathered at the top part of the storm clouds.

Electrons near the ground are repelled by the negatively charged bottom of the storm clouds, moving deeper into the ground, resulting in the objects on the surface of the ground becoming positively charged. As the negative charges build up at the bottom of the clouds, surrounding air particles are ionised, sending stepped leaders towards the ground. At the same time, the positively charged objects on the ground also ionise the air particles around them, sending streamers upwards towards the clouds.

When a particular stepped leader and streamer meet, a path is established, and the huge potential difference between the cloud and the object results in a massive current flow.

This huge current flow produces an enormous amount of heat, up to 30 000 deg C, which appear to us as the brilliant white-blue flash of a lightning flash.