With all this talk about lightning we thought it only fair to acknowledge all the noise behind the light show. Thunder is not only a side effect of lightning but can provide a great safety tool in a storm. Allow us to explain.
First, the intense heat from the lightning causes the air to expand.
Then the heated air cools and rapidly contracts.
That quick expansion and contraction causes the air to move back and forth giving us intense sound waves, AKA thunder.
And, that rumbling effect you may hear at times are the sound waves coming from different parts of a jagged lightning bolt reaching you at slightly different times.
Now, the important part what to do with this information. As you know the thunder almost always lags behind the lightning display. As soon as you see the lightning, count the seconds until you hear the thunder (and we're talking those slow "mississippi" seconds). Since sound travels at nearly 1,000 feet per second, if there are 5 seconds between between the flash and the boom, it means the lightning is about a mile away. If you see the lightning and hear the thunder at the same time, watch out, the storm is right above you. In other words, RUN.