A 1-km Multi-ICs/BCs and Mixed-Physics WRF Ensemble for Sea-Breeze Convection Prediction during ESCAPE: Precipitation Evaluation

Abstract Accurate prediction of precipitation by sea-breeze convection (SBC) remains a challenge for operational numerical weather prediction (NWP) models. A set of 24-h, 1-km, 48-member ensemble forecasts using the Weather Research and Forecasting (WRF) Model was produced for the Experiment of Sea Breeze Convection, Aerosols, Precipitation, and Environment (ESCAPE) campaign in June 2022, around Houston, Texas. The 48-member WRF ensemble consists of three initial conditions (ICs)/boundary conditions (BCs), four microphysics schemes, two planetary boundary layer (PBL) schemes, and two aerosol loadings. Precipitation forecasts were verified against observations along the Texas and Louisiana coastlines for eight SBC cases. The 1-km WRF ensemble outperforms deterministic operational models in predicting SBC precipitation due to its 1-km horizontal grid spacing and ensemble approach. Adding varied ICs/BCs to the 1-km mixed-physics ensemble improves light-to-moderate precipitation forecasts but not necessarily heavy rainfall (>99th percentile) forecasts. Moreover, moving from 3- to 1-km horizontal grid spacing reduces SBC precipitation biases and increases fractions skill scores. Finally, WRF members with the High-Resolution Rapid Refresh (HRRR) ICs/BCs, the Mellor–Yamada–Nakanishi–Niino (MYNN) eddy-diffusivity mass-flux (EDMF) PBL scheme, the Thompson microphysics scheme, and a high aerosol loading generally show better precipitation forecasts. Our results collectively 1) demonstrate the benefits of using a 1-km convection-allowing ensemble to improve SBC precipitation forecasts and 2) advocate for continued development of physics parameterizations to address precipitation forecast biases. Significance Statement Accurate predictions of the location and timing of sea-breeze convection are challenging for operational weather prediction models, especially for complex and heterogeneous environments. Using an ensemble approach with multiple initial conditions/boundary conditions and different physics configurations, we evaluated a 1-km weather model’s ability to predict sea-breeze convection around Houston, Texas. Our findings provide guidance on the model physics configuration for predicting convective precipitation by sea breezes and underscore the potential for improved precipitation forecasts via further refinement of horizontal grid spacing for current convection-allowing ensemble systems.