Meteorology. Lightning strikes at the north entrance of Yellowstone National Park in Wyoming. Lightning occurs when a large electrical charge builds up in a cloud. In cloud-to-ground lightning a "leader" of electrons first descends to the ground. As soon as it makes contact, an enormous return stroke surges up the ionized path left by the leader, producing instantaneous temperatures as high as 30,000 Celsius. The massive release of energy during the return stroke produces the luminous bolt seen by the naked eye.