Development of Surface Data Assimilation and Forecast for Rapid Refresh Forecast System

The Rapid Refresh Forecast System (RRFS) is NOAA’s next generation regional convection-allowing 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. RRFS is targeted to replace many current regional and storm scale operational NWP systems such as High Resolution Ensemble Forecast System (HREF), Rapid Refresh (RAP), High Resolution Rapid refresh (HRRR), North American Mesoscale Forecast System (NAM) + nests, etc.

The forecasts for surfaces are the most important fields that RRFS try to improve, through high frequency data assimilation of the surface observations, based on the successful experience from development and implementation of RAP/HRRR. The functions that are used for RAP/HRRR surface data assimilation were developed to work with the FV3LAM interface, such as using terrain-elevation matching surface temperature observations, soil T/Q adjustment based on the lowest level analysis increments, continue surface cycling, using 2m T/Q from model as background in the GSI analysis, and soil surgery to initialize the soil fields from RAP/HRRR soil. The real-time vegetation fraction, snow/sea ice coverage, and SST are updated daily in the system. Retrospective experiments were conducted to study the impact of those functions in the RRFS system. The results will be reported at the conference.