Updates to the MYNN-EDMF PBL Scheme to Improve Operational Forecasting Applications

The Mellor–Yamada–Nakanishi–Niino (MYNN) Eddy Diffusivity-Mass Flux (EDMF) moist-turbulence parameterization scheme has been an important component of the Rapid Refresh (RAP), High-Resolution Rapid Refresh (HRRR), and has been slated for the first version of the Rapid Refresh Forecast System (RRFS). More recently, its development focus has expanded to include global applications. Most of the recent updates have been developed within the CCPP/FV3 framework but recent attempts to unify the scheme for non-CCPP frameworks allows for more easy and frequent updates in the future.

The long-awaited updates for WRF-ARWv4.5 help alleviate several concerns that have been noticed by some colleagues and some that have escaped the eye of the novice. One of the most crucial improvements has been to improve the conservation properties, which were a primary cause of poor performance in initial testing for medium-range forecasting in the global framework. These conservation issues were well hidden in short-range regional applications. The MYNN-EDMF has recently received focused attention for hurricane applications in hurricane forecasting, and has shown reasonable skill. Other improvements have come through the refinement of the subgrid-cloud representation of both stratus and shallow-convective regimes. A new closure level “2.6” was added to improve the representation of stratus clouds, while new relationships derived from large-eddy simulation analysis have improved the shallow-cumulus clouds. Furthermore, the MYNN-EDMF has recently received focused attention for hurricane applications in hurricane forecasting, and has shown reasonable skill. Several bugs have been removed to allow for an accurate TKE budget analysis and additional capabilities have been added, such as the capability to mix snow and black-carbon aerosols. These recent developments will be overviewed and some examples of improvements will be given. Further development plans will be outlined.