A new version of the Rapid Update Cycle (RUC) is being implemented into operations at the National Centers for Environmental Prediction (NCEP) in April 2002. This new version includes a doubling of horizontal resolution (40-km to 20-km), an increased number of computational levels (40 to 50), and improvements in the analysis and model physical parameterizations. A primary goal of the 20-km RUC (or RUC20) is improvement in quantitative precipitation forecasts for warm and cold seasons. Improvements in near-surface forecasts and cloud forecasts have also been targeted. The RUC20 provides improved forecasts for these variables, as well as for wind, temperature, and moisture above the surface.

The key enhancements to the RUC20 assimilation of observations are 1) an improved optimal interpolation (OI) analysis and 2) the assimilation of GOES cloud-top pressure, as discussed below. The most important changes in the RUC20 OI analysis are the observation preprocessing and a more intelligent matching to background values for surface temperature and dewpoint, near-surface rawinsonde structures, and precipitable water observations.

The RUC20 forecast model is also significantly modified from the RUC40 version, including the following: · Grell/Devenyi (2001) convective parameterization, with ensemble approach to closures (driving parameterized convection) and feedback. · Improved linkage between convective parameterization and other components of the RUC model. · Modified version of Smirnova-RUC land-surface parameterization (Smirnova et al. 2000a) including frozen soil processes and two-layer snow model. · Upgraded RUC/MM5 mixed-phase cloud microphysics (Brown et al. 2000), with improved representation of supercooled liquid water and reduction of excessive amounts of graupel. The microphysics is now called with a 2-min time step in RUC20 instead of the previous 10-min time step.

The presentation will include case study comparisons with the RUC40 and also overall verification statistics from warm, cold, and transition seasons.