In these practice sketches, I tried several different techniques. First, I only partially removed the liquid mask. This resulted in a stippling effect in some of the clouds. I also laid down a second blue wash on the sky. I tried different ways of sculpting the clouds with gray and black pigments.
In the second sketch, below, I used a darker blue as a second wash. I laid down a small landscape at the bottom of the sketch, for scale.
Here is the reference photo: