Why does thunder seem to rumble on for a long time after a lightning strike?

The rolling sounds of thunder are some of the most amazing sounds nature produces.  But how do they get that rolling sound?  Well it all has to do with the speed of sound.  The speed of sound in air is about 770 mph, or 1129 ft/s.  This is a variable speed, based on perfect atmospheric conditions.  Of course in a thunder storm, conditions aren't perfect...  Anyhow, if you have ever had a lightning bolt strike close to you, you will be familiar with the fact that it sounds very different up close.  A close strike sounds like an explosion or gunshot, a very loud bang, followed by the telltale rumbling afterwards.  Therefore you should know that, anywhere along the path of lightning, the lightning will sound like this.  Even up in the clouds, it sounds as if it was a loud single bang.  Now, storm clouds can range from anywhere from 1,000 ft above the ground, to 16,000 ft above the ground.  Even in the smallest cases, the sound from the top of a lightning discharge that started only 1,000 feet from the ground, will take almost a full second more to get to your ears, then the sound generated by the same bolt as it hit the ground.  This is the same all the way up the bolt, as the bolt extends upwards, the sound from the bolt takes longer and longer to reach your ears, thus making the very unique sound which is rolling thunder.  Not only is height a factor here, however.  Distance is as well.  Sometimes lightning will spread out for miles inside a cloud as well as striking the earth at a specific spot.  This distance is often why you will hear thunder fade away from a strike, and then suddenly get louder.  The strike may have been far away, but the bolt traveled closer to you in the clouds.

I hope I have been able to explain this in a way that people understand, feel free to email me if you have any questions :)  I will add them to this blog and try to answer them :)