Evaluation of severe weather forecasts from real-time medium-range convection-allowing ensembles over the conterminous United States Weather and Forecasting

During both spring 2023 and 2024, we produced two sets of experimental, real-time, medium-range (3–8-day) convection-allowing ensemble (CAE) forecasts with variable-resolution global models that had 3-km horizontal cell spacing over the conterminous United States (CONUS). One ensemble had 10 members, produced 8.5-day forecasts, and used GFDL’s C-SHiELD, a prediction model based on the Finite-Volume Cubed-Sphere Dynamical Core. The second ensemble had 5 members, produced 5.5-day forecasts, and used NSF NCAR’s Model for Prediction Across Scales (MPAS). These demonstrations collectively represented the first real-time, medium-range CAE guidance over the CONUS and the first real-time CAE forecasts produced with variable-resolution global numerical weather prediction models.