Studying Vortex-SE Weather Events By Comparing a Scale-Aware PBL Scheme in the HRRR Model at Varying Resolutions to Observations

The VORTEX-SE project was conducted to improve understanding of the conditions that produce tornadoes in the Southeast US. We run retrospective simulations with the RAPv4/HRRRv3 mesoscale model and compare forecasts to CLAMPS (Collaborative Lower Atmospheric Mobile Profiling System) and other measurements for several weather events studied during March and April in the 2016 VORTEX-SE campaign. We evaluate the model at multiple horizontal resolutions (3km and higher) using an updated scale-aware version of the Mellor-Yamada-Nakanishi-Niino (MYNN) Planetary Boundary Layer (PBL) scheme. This scheme activates up to ten different plumes with diameters 100 to 1000m (depending on model grid spacing) under convective conditions, adds mass-flux calculations to better parameterize the non-local turbulent transport associated with updrafts/plumes, and varies the magnitude of the areal fraction of the updrafts. Much of the variation of these quantities lies between 3 km and 300 m grid spacing, so the multiple nested testing framework in support of 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.