Here is a quick way to change the snow value in CTS (Complete Terrain Shader), without installing the weather manager.
GameObject terrainGO = GameObject.Find("Terrain");
Terrain terrain = terrainGO.GetComponent();
Material material = terrain.materialTemplate;
I needed this to be able to add the look and feel of the volcano ashes. This parameter “_Snow_Amount” will be slowly incremented after the eruption phase.
Here is a quick peek at the terrain covered in ashes: