Step-by-step: Illustrate clouds realistically
1Establish a perspective grid. Clouds are 3D forms that should follow the scene’s perspective line. Clouds typically travel along the same plane level, so they should line up on a single perspective plane. Treat the clouds as if they are solid objects with top, bottom and side planes.
2Use an airbrush to block out the shape of the clouds very loosely. Keep in mind which direction the sun is shining to keep the lighting and cast shadow consistent. Start erasing away the edges to shape the silhouette and use the texture brush to define the inner forms.
3Define the form to finish. Using a texture brush, look for areas within the blocked-out shapes where you can drop some darker tones as well as brighter highlights to increase the contrast level. Clouds that are further away from you will have less contrast than closer ones.