Why does the sky rumble during a thunder storm?
it is the sound waves produced by the electic discharge. In a fraction of a second the air is heated to a temperature approaching 28,000 °C (50,000 °F) by lightning. This heating causes it to expand outward, plowing into the surrounding cooler air at a speed faster than sound would travel in that cooler air. The outward-moving pulse that results is a shock wave, similar in principle to the shock wave formed by an explosion, or at the front of a supersonic aircraft. The gentle rumbles are you hearing those explosions in are ripple effect the further away you are the less the sound is. The closer the storm is to you the louder the boom is. Imagine a stone into a puddle. The ripples go outwards, now drop another onto the same puddle and the rings overlap. If you were listening to sound waves instead of watching water waves you would have the same effect. Depending on where you are in relation to the expansion of the air and shockwave it produces you either hear a loud bang or a subtle rum
