A major revision to the Rapid Update Cycle is being implemented into operations at the National Centers for Environmental Prediction (NCEP) in early 2002. This new version includes significant changes in horizontal (40km to 20km) and vertical (40 levels to 50 levels) resolution, and to analysis and model techniques. The assimilation changes include an improved optimal interpolation analysis with improved treatment of surface observations and a cloud analysis in which GOES cloud-top data is combined with the RUC 1-h 3-d explicit cloud/hydrometeor forecast fields. The model changes include major modifications to the RUC/MM5 explicit mixed-phase cloud microphysics and RUC land-surface model, and introduction of an ensemble-closure based cumulus parameterization developed by Grell and Devenyi.

Overall, extensive verification results indicate improved performance from the RUC20 vs. the previous 40-km RUC over a wide range of parameters, including precipitation, cloud, and surface forecasts, and also forecasts of state variables such as wind, temperature and relative humidity. The implementation of the RUC20 sets the stage for further improvement in various aviation products which are dependent on the RUC, including those for inflight icing, turbulence, and convective weather.