IMPLEMENTATION OF THE CLOUD PREDICTION SCHEME IN THE ETA-MODEL AT NCEP

An explicit cloud prediction scheme has been developed and incorporate d into the Eta Model at the National Centers for Environmental Predict ion (NCEP) to improve the cloud and precipitation forecasts. In this s cheme, the cloud liquid water and cloud ice are explicitly predicted b y adding only one prognostic equation of cloud mixing ratio to the mod el. Precipitation of rain and snow in this scheme is diagnostically ca lculated from the predicted cloud fields. The model-predicted clouds a re also used in the model's radiation calculations. Results from the p arallel tests performed at NCEP show improvements in precipitation for ecasts when prognostic cloud water is included. Compared with the diag nostic clouds, the model-predicted clouds are more accurate in both am ount and position. Improvements in specific humidity forecasts have al so been found, especially near the surface and above the freezing leve l.