Water and ice move around inside the cloud; forced up by warm air currents, down by gravity, and compressed in the cloud. Just as rubbing a balloon can create static electricity, the particles in the cloud become charged. It’s not clear how it happens, but charges separate in the cloud. Positive charges move up, and negatives move down.Once a significant charge separation has built up, the positive and negative charges seek to reach each other an neutralise. ‘Streamers’ come up from the ground to form a pathway. Once a pathway is completed a spark forms, neutralizing the charge.As the negative charge races down, the air surrounding it heats up.The spark is very hot at almost 20,000 degrees Celsius, and it rapidly heats the air to create a shock wave.