Partial Cloudiness in Microphysics Schemes

When the grid size is large in a weather forecasting system it is natural that clouds and precipitation can be generated in parts of a grid. However in some of the microphysics schemes the grid can only be either cloudy or clear and no partially cloudy is allowed. This will lead to biases in the initiation of the clouds and amount of the clouds and consequently the initiation and intensity of the precipitation. This study illustrates how a partial cloudiness scheme is added to a microphysics scheme and how it affects the results in a SCM and the FV3GFS. In particular, it demonstrates that for simple microphysics schemes it is possible to analytically derive the effects of the partial cloudiness on the cloud and precipitation forecast.