The Rapid Refresh: Operational Upgrade to Version 2 at NCEP and Further Development Toward Version 3

An upgrade to the NCEP operational Rapid Refresh (RAP) weather prediction system is planned for late 2013 or early 2014. This upgrade to version 2 of the RAP (RAPv2) will include a number of significant enhancements to both the data assimilation and model prediction components of the RAP. Work is also progressing on further enhancements to the system that are being incorporated into a real-time experimental version 3 of the RAP (RAPv3), being run by GSD.

Within the data assimilation module, the most significant improvement for RAPv2 is the upgrade from a traditional 3DVAR assimilation technique to a hybrid ensemble technique, using covariance information from the 80-member global ensemble data assimilation system. This change, enabled by global assimilation developments and facilitated by use of the community-based Gridpoint Statistical Interpolation (GSI) analysis package, has resulted in significant forecast improvement for most upper-air variables and forecast lengths. Additional assimilation enhancements include improved cloud analysis and soil temperature and moisture adjustment procedures.

Within the WRF-ARW model component, the most significant enhancements include switching from the MYJ planetary boundary layer (PBL) to a specially adapted MYNN PBL scheme, an upgrade from a 6-layer to a new 9-layer version of the Smirnova (RUC) land surface model formulation (LSM), and a modified roughness length specification. There are also smaller upgrades to other model components, including the Thompson microphysics and the radiation schemes.

A number of model and assimilation changes are under evaluation for RAPv3, which will be frozen for the 2014 warm season evaluation in March 2014. These include upgrades to the new Grell-Freitas cumulus parameterization, upgrade to a new Thompson scheme that incorporates aerosols, enhancements to the satellite radiance assimilation (bias correction and more data types assimilated), and other assimilation improvements (adding radial velocity data and mesonet data, aircraft temperature bias correction, etc.) In the presentation, RAPv2 enhancements and the associated forecast improvements will be described in detail, followed by a summary of the ongoing work toward RAPv3