|Fig: Physics of Lightning|
Storm clouds contain ice particles. These ice particles rub against each other and lose electrons. As the particles lose electrons they become charged. These charged ice particles accumulate and develop huge areas of charge within the cloud. The charge in these areas builds up until it eventually discharges into other areas of opposite charge or to the ground. As the charges move through the air they heat the air molecules causing the air to glow(lightning). As the air heats up it expands and creates the mighty roar of thunder that we hear after every lightning bolt.