We introduce Lagrangian framework for the cloud physics and rendering at landscape size. Cumulus clouds are ubiquitous in outdoor naturalistic scenes. However, realistic and scalable cloud simulation continues to be a challenge in computer graphics. Computational fluid dynamics models (CFD) are computationally intensive and hence impractical for real time methods. Eulerian models [Harris et al. 2003] on the other hand require modeling even the transparent volume, placing serious restrictions on the domain size. More importantly, both these methods do not offer convenient handles on initial, border and atmospheric conditions which play a key role in the natural evolution of the cloud phenomena. We introduce Lagrangian framework for the cloud physics and rendering at landscape size. The use of Lagrangian formalism, aerology physics, and separation of environment from the dynamics, brings more robustness, offers meaningful high-level handles for user control - environment profile and evolution, cloud base and top.