The stark contrasts and pure colours of winter skies are beautiful, but give you less time to paint them directly from observation than summer skies do. For that reason, paint from a photo for your first winter sky paintings. After you paint several skies, you will be able to start inventing your own sky scenes, which means to paint them from imagination with a degree of realism. Also, test your colours on a spare piece of drawing paper before applying paint to your main canvas.
Find and print a colour photo of a winter sky that includes other elements evoking the ideas of winter and sparseness. Example images include bare treetops, snow-covered roofs and streaming clouds. If you cannot find a single photo, combine several with the aforementioned elements into a single image with a digital painting program.
Sketch in pencil the reference photo's image onto your canvas. This produces the underpainting, which guides your eye in creating the main painting.
Squeeze a dollop of blue pigment onto your palette. With a palette or plastic knife, mix white or black pigment with the blue, until the pigment's value --- its lightness or darkness --- is slightly lighter than a region of the reference image. Paint darkens when it dries. Repeat this step for the remaining blue regions of the photo to produce a range of values matching the photo.
Wet down the pure pigment by applying at least five drops of water to it with an eyedropper.
Dip the largest usable brush into one of the dollops. Apply the pigment to the canvas in flowing, even strokes. Repeat this step for the remaining blue regions in the photo, then let the blue regions dry. Or, blow-dry them with a handheld hair dryer.
Squeeze violet or orange onto the palette, depending on which your reference photo displays. Violet will come premixed in a tube, but you will probably have to make orange. To do so, mix dollops of red and yellow together with a palette knife.
Dip a brush in the pigment, then apply it in a sweeping arc to the appropriate region on your canvas.
Sweep another brush filled only with water immediately, across the fringes of the region you just painted. Quickly but smoothly stroke these fringes toward the unpainted parts of the canvas, away from the regions that have the greatest saturation. This will produce a smooth gradation from the orange or violet pigment to the background blue. This step completes the background. Now you will paint the more delineated foreground elements.
Mix the paint for the regions of a particular foreground element such as tree branches, rooftops or clouds. Use the instructions from the sky painting steps to guide you.
Apply the paint to the canvas, using the blending technique used in Step 8 for the orange or violet. Be sure to paint the more transparent values first, followed by the less transparent values. Your pigment containers will indicate the transparency level. White and black usually have no transparency.
Repeat the previous two steps for the remaining foreground elements to complete the painting of the winter sky.