A Prognostic Cloud Scheme for Operational NWP Models

An explicit cloud prediction model has been developed and incorporated into the Eta Model at the National Centers for Environmental Prediction. In this scheme, only one predictive variable, cloud mixing ratio, is added to the model’s prognostic equations to represent both cloud liquid water and cloud ice. Precipitation is diagnostically calculated from cloud mixing ratio. Extensive tests have been performed. The statistical results show a significant improvement in the model precipitation forecasts. Diagnostic studies suggest that the inclusion of cloud ice is important in transferring water vapor to precipitation and in the enhancement of latent heat release; the latter subsequently affects the vertical motion field significantly.