Watercolor can create expressive, moody skies perfect for describing stormy skies. The wet on wet and stroke and bleed techniques create convincing effects. The wet on wet technique is presenting the paper surface so that subsequent strokes form soft edges. The stroke and bleed technique involves making a brush stroke of fairly heavy pigment on a wet surface, then tipping the paper so that gravity pulls the pigment downward, suggesting rain falling from a cloud. By rotating the paper, you can change the direction that the paint bleeds, suggesting rain blown at a diagonal by the wind.
Here is how these techniques might be applied in a watercolor of a rainstorm in Yosemite Valley. Click on the first image to start a step-by-step slide show.
Start with a line drawing of the landscape before you. Use negative shapes, such as the distance between the cliffs to help ensure accurate proportions.
Lighten the background with a kneaded eraser.
Apply a wet gray wash over the pencil drawing.
While the paint is still wet, begin to apply rainclouds with the stroke and bleed technique.
Add more layers of clouds and rain, maintaining the angle of the paper.
Let the sky dry. Then begin adding the distant cliffs. Avoid detail and keep the background low contrast and a light value.
With slightly darker paint, add the next layer in the middle ground.
Once the previous layers are dry, add the foreground cliffs with darker paint. Note that these cliffs have some contrast and detail.
To create the effect of rain in front of dark cliffs, rewet some of the paper and lift out paint with a clean brush or paper towel. You may not be able to effectively lift our some types of paint or on some types of paper. Try test swatches before attempting this on your painting.
Add the Trees on the valley floor. A subtle jiggle of the brush suggests distant trees.
Add a little hint of green to some of the foreground trees. You can suggest foreground raindrops with rapid diagonal strokes of a white gel pen.
The previous stage suggested a storm that is clearing in the distance. A heavier coat of gray throughout obscures more of the background and gives the sense of an unrelenting downpour.