Anyone who lives in northerly climes is familiar with the many variations of snow — dry and powdery, heavy and wet, or just a slushy, muddy mess. If you want to model a mess, follow these steps.
You’ll need Winsor & Newton Acrylic Gloss Medium gel (or equivalent), Woodland Scenics Snow (No. SN140), Hudson & Allen Studio Slush (No. 9605), and Pledge Floor Gloss (PFG) or equivalent.

Mask mounting holes for figures in your completed groundwork and other areas you want to protect from the slush effect, like tire tracks that would press through the slush.

Place your model in a confined area like a shallow box or pan — this will be important when the snow begins to fly because it contains the mess. Then, working in sections, cover the groundwork with the acrylic gel medium using a large brush.

Mix the slush and snow material to obtain a mixture that looks right for the effect you want and sprinkle it into the gel medium before it dries. I use a small palette knife to push the mixture into the gel medium and move it around a bit creating higher and lower spots.

When applying the acrylic gel medium in tight areas or places you don’t want to completely cover, like this section of tall grass away from the roadway, use a smaller brush.

Use your artistic eye. For example, I used Woodland Scenics Snow to differentiate the muddy slush on the road from the snow away from it. I just mixed a little snow into the gel medium and brushed it into the grass.

After the first layer of slush is dry, build up the areas where slush would normally accumulate (like tires plowing through snow) by adding more gel medium and your snow-slush mixture. Scrape the slush mixture off any areas you’ve masked to ease removal later.

You can also scrape away material to show footprints in the slush.

To make the slush look slushier, apply PFG with an eye dropper. You can see the difference between the area covered with PFG and area that is not. The PFG ties it all together to give it that wet, heavy look.

Here, you can see the difference between the road where the slush mixture was added as opposed to the grassy areas where only the snow was applied. The spots without snow or slush are intentional for the scene.

Make sure you also get a bit of slush on vehicles and figures in your scene. Just apply the gel medium premixed with the slush mixture and touch it to the appropriate spots.