We propose a method to create a realistic snow accumulation effect in screen space for realistic natural environment rendering. Existing algorithms are not suitable for low-polygon terrain because they need high-resolution features on the surface. We develop a technique to enhance the resolution of the surface's normal as geometrical features by extracting details from a decal texture of a terrain model. Our algorithm is implemented on GPU totally, and since it works as a postprocessing effect, it can be performed in the real-time calculation. Moreover, it is not dependent on the size and shape of the terrain. Our algorithm can be easily integrated into a common real-time rendering engine and can be applied a various type of terrain data which has decal textures.