A 13-km RUC AND BEYOND: RECENT DEVELOPMENTS AND FUTURE PLANS

With the next upgrade to the NCEP computer, there will be the capability to run operationally an improved version of the Rapid Update Cycle (RUC) at higher horizontal resolution. Our current plan is to go to a 13-km horizontal grid spacing from the current 20km, while continuing with 50 levels in the vertical, with the same hybrid-isentropic vertical coordinate used in the current RUC20. In addition to changed resolution, RUC will improve its physics, particularly the Grell-Devenyi parameterization of convection and the grid-scale NCAR mixed-phase bulk microphysics scheme. An early version of RUC13 has been under test at FSL since late 2003, and this summer the RUC13 model will be coupled with a 13-km version of the RUC 3DVAR in a 1-h intermittent assimilation cycle to provide 48-h forecasts in support of the NOAA New England High-Resolution Temperature Program. We anticipate operational implementation at NCEP during 2005.

The chief benefits of the higher resolution RUC13 will be in better forecasts of terrain-induced flows and near coastlines, resolved clouds, and convective and resolved-scale precipitation. Improvements evident in cloud and precipitation forecasts during initial testing result from both revised microphysics and convection parameterizations as well as higher spatial resolution. These changes in the RUC13 are considered to be quite significant for aviation and severe weather forecast users.

At the conference we will compare FSL's RUC13 performance to that of a RUC20 cycle using the same observational input. In addition, we will discuss the proposed roadmap to the next operational version of the Rapid Update Cycle, called Rapid Refresh, which will run in the WRF framework at a horizontal resolution of about 10 km, likely using one of the two non-hydrostatic WRF dynamical cores, and incorporating the Gridded Statistical Interpolation 3DVAR analysis under development at NCEP. Operational implementation of this version is planned for 2007.