Heat lightning: Inaudible and repeated flashes of lightning within a thunderhead at twilight on a hot summer night. Typically, heat lightning is simply too far away for thunder to be heard. But as a lightning photographer, I've also experienced intracloud lightning at close range that is virtually silent. I've heard sounds accompanying overhead flashes that resemble the sizzle of water hitting a hot frying pan, with no clap of thunder. Tucson, Arizona. Digital