This paper presents an efficient, physics-based procedural model for the real-time animation and visualization of cumulusclouds at landscape size. We couple a coarse Lagrangian model ofair parcelswith a procedural amplification using volumetricnoise. Our Lagrangian model draws an aerologyi.e.,the atmospheric physics of hydrostatic atmosphere with thermodynamicstransforms, augmented by a model of mixing between parcels and environment. In addition to the particle-particle interactions,we introduce particle-implicit environment interactions. In contrast to the usual fluid simulation, we thus do not need to samplethe transparent environment, a key property for real-time efficiency and scalability to large domains. Inheriting from the high-level physics of aerology, we also validate our simulation by comparing it to predictive diagrams, and we show how the user caneasily control key aspects of the result such as the cloud base and top altitude. Our model is thus fast, physical and controllable.