As a result, the ascending ice crystals become positively charged and the descending hail negatively charged, causing the buildup of a positive charge at the top and a negative charge in the middle of the thundercloud. In the part of the thundercloud with an air temperature above
-10ºC and close to the earth, water droplets adhere to the surface of the hail, forming a water layer. There are now H+ ions within the hail and low mobility OH- ions within its surface water.

When hail in this state strikes ice crystals, the ice crystals strip off the OH- ion water layer on the surface of the hail and then rise up, leaving the remaining hail with a positive charge.

In this manner, the insides of thunderclouds turn into something like an electric power plant, with positive, negative, and positive layers. Within this electric power plant flows a voltage of hundreds of millions of volts and an instantaneous electric current in the tens of thousands of amperes. When this current flows, extremely high temperatures are produced because electric current has an inherent difficulty in passing through the atmosphere. The light generated by the resulting heat appears as lightning.