Surrounding air superheats to more than 18,000 degrees Fahrenheit, expands outward rapidly and produces the strong soundwaves known as thunder when the electrical energy of lightning is discharged in Earth's atmosphere. Most of the energy of lightning is in the form of heat that quickly dissipates in cooler air. Before lightning strikes, the insulating capacity of air breaks down, and the negatively charged atmosphere produces powerful bolts.
The flash of lightning temporarily equalizes the charges in the atmosphere until water particles build up negative charges of electrons again. Negative charges build up in clouds due to water droplets and ice crystals rubbing against each other to produce negative charges. The ground is positively charged, and the atmosphere produces lightning to balance the charges.
Scientists have repeatedly measured physical properties of lightning. The phenomenon ranges in temperature from 18,000 to 70,000 degrees Fahrenheit. A single lightning bolt is usually between 1 and 2 inches wide and contains between 100 million and 1 billion volts of electricity. The color of the discharge depends upon the surrounding environment, but flashes are normally white or blue-white. The shockwave produced by lightning accelerates outward faster than the speed of sound for 30 feet surrounding the bolt. Sound then slows down enough to be heard by humans as thunder.