Thunder and lightning often occur together during thunderstorms due to the electrical processes that take place within storm clouds. When the conditions are right, clouds become charged with electricity, leading to the formation of lightning. This sudden discharge of electricity heats the air around it to intense temperatures, causing an explosive expansion that creates sound waves—what we hear as thunder.
Lightning is essentially a giant spark of electricity, and it can happen in various forms, such as cloud-to-ground or cloud-to-cloud. Regardless of the type, the lightning strikes create a rapid increase in temperature, sometimes reaching up to 30,000 degrees Fahrenheit. This explosion causes the air to expand quickly and creates a shockwave, which travels outward as sound, hence producing thunder.
Because of the speed at which light travels compared to sound, we see the flash of lightning before we hear the rumble of thunder. As a rule of thumb, for every five seconds between seeing the lightning and hearing the thunder, the storm is approximately one mile away. This relationship is a natural consequence of the physics of sound and light.