SEATTLE - Many wondered if last Thursday's storm was heat lighting. Many people in the Midwest have probably heard the term refer to a type of lightning that occurs on hot days that doesn't have any thunder associated with it. That was the case in the early stages last week when thousands could see lightning to the east, but not hear it.
But "heat lightning" really doesn't exist -- at least, not as a special kind of lightning. The reason you would not hear the thunder is simply because the lightning strike was too distant for you to hear it.
Light can travel much greater distances than sound, so if the lightning bolt is far enough away (say, over 10 miles), you'll see the flash, but the air will have long absorbed the sound of thunder before it reaches you. In last Thursday's case, the storms were so tall, the lightning could be seen for several miles.