Oh how I do love drawing clouds! And trees! And silhouettes! This is the sky over Long Beach. I figured it was LA at first (when I was looking through source images on my phone) but with closer inspection I realized that the trees are too straight to be LA trees, and those sticks at the bottom are the tops of the sails of ships. I took the original photo when I was visiting my family in Seal Beach. I suppose the sky is pretty all over.
The line drawing below is actually much simpler than the one used to guide the colors/create the shapes in the final image. I started drawing and filling as I went instead of keeping the layers separate (Photoshop talk).