Deep moist convection creates a rich variety of cloud structures on many different length scales, including the familiar weather phenomena of squall lines and hurricanes. Comprehensive Cloud Resolving Models would include water substance in all of its phases: vapor, liquid and ice. Furthermore, liquid water would be separated into cloud water and rain water. Here we take a minimalist approach by incorporating cloud microphysics in the limit that the time scales associated with condensation, auto-conversion and evaporation are small compared to other relevant time scales in the problem (advection, buoyancy, rotation, rainfall). Conservation laws for momentum, energy, moist entropy, and total water are all retained, but have a simple nontrivial form. Dependence of the minimal model on rainfall speed will be discussed, and in particular, the stability/instability boundaries for saturated regions.
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