38HYDRO Recent Developments of the 200-Member West-WRF Near Real-Time Forecast Ensemble

The Center for Western Weather and Water Extremes (CW3E) has developed a customized version of the Weather Research and Forecasting model (WRF), named West-WRF, that is run in near-real-time (NRT) forecast mode in support of decision making and scientific research of extreme weather events over the Western U.S. The West-WRF NRT framework is used to generate a 200-member ensemble that provides gridded model forecasts tailored for the representation of atmospheric rivers and Western U.S. precipitation. This season it is run daily from September through March with a 0000 UTC initialization out to 7 days forecast lead time. A single 9-km domain covers much of Western North America and the Northeastern Pacific Ocean. A 60 vertical level configuration has been customized for optimal resolution of atmospheric river processes. A combination of initial and lateral boundary conditions from the Global Ensemble Forecast System (GEFS) and European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble are used to initialize the ensemble. Additional ensemble sampling of forecast uncertainty is achieved through multi-physics (100 unique combinations) and stochastic kinetic energy backscatter (SKEB) perturbations. This season (2023-2024), a set of terrain height perturbations have been integrated into the West-WRF NRT ensemble, using different methods of terrain interpolation, smoothing functions, and number of smoothing passes. The development, testing, and implementation of these terrain perturbations into the West-WRF NRT ensemble will be discussed.