In all my interviews, I usually say I write the story before I draw the pictures. An exception to this was the cover of Where the Mountain Meets the Moon, where I drew my idea for the cover long before the book was done. For "Return to Sky," the same thing is happening. Recently, this image for the cover came into my mind:
We'll see if the image makes it to the final book...when I finish it (about 1/3 left to go, I think).