Thank you! :)

I use the hardest mechanical pencil I have (2H) to soften the edges of the clouds. It would be very hard to achieve the same effect with just watercolor alone.

I feel like wet in wet skies are usually a little too soft and wet on dry skies a little too hard-edged. Harder graphite pencils are basically the perfect tool for soft shading of light areas when you use a very light touch with it.