Simulating Vortex-SE Weather Events with a Scale-Adaptive PBL Scheme in the HRRR Model at Varying Resolutions

An updated scale-adaptive version of the Mellor-Yamada-Nakanishi-Niino (MYNN) Planetary Boundary Layer (PBL) scheme has been implemented in the RAPv4/HRRRv3 model. This scheme activates up to ten different plumes with diameters 100 to 1000m (depending on model grid spacing, height of the boundary layer, and other factors) under convective conditions. The addition of the mass-flux scheme better represents the non-local turbulent transport associated with updrafts/plumes, and allows the magnitude of the fraction of the updrafts to vary. We evaluated this scheme by running retrospective simulations of the RAPv4/HRRRv3 at varying horizontal resolutions (500m to 3km) and compared output to observations collected during March and April 2016 as part of the VORTEX-SE project, which was conducted to improve understanding of the conditions that produce tornadoes in the Southeast US. Much of the variation of the parameters in the PBL scheme lie between 3 km and 300 m grid spacing, so studying the multiple nested testing framework in the VORTEX-SE campaign serves as an important opportunity to refine these many new features in the MYNN and better prepares the RAP/HRRR physics suite for a broad set of meteorological forecast applications at any spatial scale.