New insights into convection‐permitting model simulations from a ZDR diagnostic for raindrops

A polarimetric radar forward operator to simulate differential reflectivity () from rain was developed to evaluate storms in the Met Office Unified Model (MetUM). Subkilometre simulations were carried out for two case days of the Wessex Convection Experiment (WesCon) field campaign in the summer of 2023. The joint distribution of reflectivity () and followed a one‐to‐one relationship for simulations using a single‐moment microphysics scheme, in contrast with radar observations. Simulations using the Cloud AeroSol Interacting Microphysics (CASIM) double‐moment microphysics scheme reproduced a spread in values for a given reflectivity similar to observations. Vertical columns of , indicative of strong updrafts, were overly intense and high in the single‐moment simulations compared with the observations, whereas column heights and intensities in the double‐moment simulations were more comparable with observations. Vertical velocities did not vary much between the different model configurations, suggesting differences in mass distributions for different hydrometeor types. from prognostic rain can thus reveal model biases and provides new avenues for future model evaluation and development.