Data Assimilation System Testing and Development for Rapid Refresh Forecast System version 1

The Rapid Refresh Forecast System (RRFS) is NOAA’s next generation regional high-resolution ensemble forecast system under development for the National Weather Service. RRFS is jointly developed by EMC and GSL along with the wider Unified Forecast System (UFS) community. The RRFS incorporates an hourly cycled deterministic forecast system, an hourly cycled EnKF data assimilation system and an ensemble forecast system. Results from the 2023 Hazardous Weather Testbed show that the RRFS has a high bias in forecast radar reflectivity in intensity and coverage, especially in the first hours of the forecast in the mid- to late-afternoon when observed convection was well underway. The data assimilation algorithm used in the RRFS will be investigated. In particular, the impact of scale- and variable-dependent localization (SDL and VDL) in the 3DEnVar algorithm on the initial (im)balance and subsequent precipitation forecast will be evaluated. In addition, the progress of RRFS DA toward the RRFS implementation will be reported.