This paper presents a fast cloud rendering method for dynamic scenes, where cloud shapes and lighting environments dynamically change. Although the Harris method [Harris and Lastra 2001] has been widely used for static cloud rendering, it can be fatally slow for real-time applications when, for example, light directions change. By introducing the 3D attenuation buffer and re-arranging the algorithm, we improved the rendering speeds of dynamic clouds by a factor of 10--100 times. The image quality is also improved due to a finer representation of light distribution.