Recent Improvements in Rapid Refresh and High-Resolution Rapid Refresh Forecasts of Severe Convective Storm Initiation
To improve RAP and HRRR forecasts of daytime convective initiation, experimental modifications to the Mellor–Yamada–Nakanishi–Niino (MYNN) planetary boundary layer (PBL) and the Grell–Freitas–Olson (GFO) shallow-convection parameterization schemes are tested. These modifications are found to better simulate the effects of nonlocal mixing, thereby facilitating the retention of capping inversions and convective inhibition atop deepening boundary layers. Furthermore, the improved coupling of subgrid-scale clouds to the RRTMG radiation scheme is found to produce additional forecast skill in the RAP and HRRR.
Results from retrospective simulations of selected severe thunderstorm events will be shown to illustrate these performance improvements in the RAP and HRRR. Finally, ongoing physical parameterization work at ESRL will be summarized.