We faced four major challenges when creating the clouds and skies in Rio. The first challenge was making volumetric clouds that could be rendered in stereo. Previous approaches involved matte paintings and 2D cards, which lacked parallax and could not be lit correctly. The second challenge was creating an efficient workflow to quickly place clouds into lots of scenes. The third challenge, was producing highly-detailed clouds when they got close to camera. And the last major challenge was finding a way to efficiently ray trace all the clouds while keeping the memory footprint small and the render times short.