Storm with lightning, I really like taking picture of it. By taking a picture you can figure out that your are missing lot off informations with your eye. With a picture you can annalyse all the details of it. The lighting is produce by a strong discharge of energy between the sky and the earth or jump between clouds. The light and the sound are prodiuce by the air phase change from gaz to plasma (same phase in neon tube). If you want to learn how to take pictures of lightning, I recomand you my tutorial here.
This is the picture I took: