A PROGNOSTIC CLOUD SCHEME FOR OPERATIONAL NWP MODELS

An explicit cloud prediction model has been developed and incorporated into the Era Model at the National Centers for Environmental Predicti on. In this scheme, only one predictive variable, cloud mixing ratio, is added to the model's prognostic equations to represent both cloud l iquid water and cloud ice. Precipitation is diagnostically calculated from cloud mixing ratio. Extensive tests have been performed. The stat istical results show a significant improvement in the model precipitat ion forecasts. Diagnostic studies suggest that the inclusion of cloud ice is important in transferring water vapor to precipitation and in t he enhancement of latent hear release; the latter subsequently affects the vertical motion field significantly.