Working your way around the negative shapes of snow on trees is difficult to do. Erasing the light snow on branches is an easier way to quickly and intuitively draw snow on trees. For this I will use a fine tipped eraser such as the Mono Zero to carve my white areas into dark graphite.
Click on the first image to start a step-by-step annotated side-show.
Make a line of middle ground trees. These marks should be consistently inconsistent, avoiding mechanical saw-edge trees that resemble a Christmas tree farm.
Add subtle darks in the trees to suggest depth.
Using a blending tool such as a paper stomp, smudge the trees to reduce their texture (pushing them further into the background) and use the graphite now picked up on the blender to “paint” the sky and add a few shadows in the snow.
Want your snow to look white? Add something really dark for contrast. Here I push the value of the foreground trees. Note that these trees are primarily scribbles with a little detail added to the top.
Now start to carve in the snow with the fine point eraser. Start in the middle of the trees making irregular clumpy masses of snow. Think of branches suspending snow pointing toward you.
Then erase the snow out on the side branches.Ta da! Snow on trees.