Abstract: We present a new method for rendering realistic cumulus clouds in real time. The clouds in our approach consist of randomly rotated and scaled copies of a single reference particle. During the pre-processing, we pre-compute optical depth, single and multiple scattering inside the reference particle for every camera position, orientation and light direction, and store the information in the look-up tables. At run time, information from the look-up tables is used to compute the cloud shading, avoiding any ray marching or slicing. To control the level of detail, we introduce a new technique which provides high fidelity for close clouds while using a coarse representation for distant regions. In addition to this, we present a new method for blending particles. Compared to traditional alpha-blending, this method produces more accurate visual results by accounting for volumetric intersection. The method merges collection of individual particles into a continuous medium, and also eliminates temporal artifacts. Our technique is able to produce realistic images at high frame rates.