Minecraft wiki entry for Thunderstorm, associated text: When lightning strikes, all entities within a 6×12×6 region horizontally centered on the northwest corner of the target block with the bottom edge 3 below the target block are struck by lightning. Multiple passes are made over this region, so items dropped during an earlier pass may be destroyed during a subsequent pass; damage immunity usually prevents struck mobs from taking more than 5 damage. Non-solid blocks (such as redstone, torches, and snow layers) are not directly affected by lightning.