Lightning's return stroke can reach 50,000 degrees Fahrenheit. To put this blast in perspective, the surface of the sun is only about 11,000 degrees. Lightning may occur even with a clear sky overhead. A thunderstorm need only be within 10 miles for cloud to ground lightning to originate from high altitude anvil clouds. The thunder that follows the lightning bolt can be heard up to 10 miles away.
Thunder is essentially the air around the lightning exploding due to high temperature.
The sound is relative. Annual property loss in the United States due to lightning has been estimated into the hundreds of millions of dollars. Much of this damage is to sensitive electronics that suffered surge damage as a result of a nearby lightning strike. Inc. If you aren't using a Surge Suppressor on your PC, you should. The surge suppressor should have not only power connections, but ones for the telephone or network.