Displaying a natural phenomenon is effective for improving the reality of computer graphics. A display of snow especially plays an important role in expressing a sense of the season. However, since geometric modeling of the various shapes of snow by hand is very troublesome, it is desirable that snow coverage shapes be automatically generated by simulation. This paper proposes a high-speed modeling technique of snow coverage. This technique takes account of the following three conditions: "snowfall blocked by an object," "irregular motion of falling snow," and "drifting snow." It applies the shadow buffer method to detect an object which blocks snowfall, calculates the influence of irregular motion of snow, and then determines the final snow-covered shape by moving the snow to a stable position.