Weather Talk: Thunder in thunderstorms is the sound of lightning
By definition, the key element in a thunderstorm is thunder. But thunder is really just the sound of lightning.
Lightning is an electrical discharge between oppositely charged parts of a cloud or between a cloud and the ground. The lightning flash is really about four pulses, each lasting approximately 30 microseconds. These surges heat the air to about 20,000 degrees Celsius, which is about three times hotter than the sun.
This dramatic heating causes the air to suddenly expand, sending a shock wave rolling out across the sky that forms an acoustical wave we hear as thunder. Because light travels faster than sound, it is possible to estimate how far away lightning is by counting the seconds from flash to thunder and dividing by five. The result is how many miles away the lightning is.