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A three-dimensional convection model has been constructed. Experiments were conducted with the model on the development of convection in a dry adiabatic environment. It was found that by using a variable diffusion coefficient, dependent on the deformation of the velocity field, many of the properties of laboratory thermals could be simulated. The same turbulence formulation was adopted for a study of non-precipitating clouds. By a suitable choice of an initial disturbance in the humidity field, it is possible to simulate many of the features of real clouds quite well. It is confirmed that vertical shear has an inhibiting effect on cloud growth. In addition, it is shown that there are significant differences in the development of a convective cloud in the presence of shear if the flow is restricted to two dimensions from the case when a three-dimensional circulation is permitted.