The June 2012 North American Derecho: A Testbed for Evaluating Regional and Global Climate Modeling Systems at Cloud-Resolving Scales

In this paper, we introduce a testbed for evaluating and comparing climate modeling systems at cloud resolving scales using hindcasts of the June 2012 North American derecho. To demonstrate its utility for model intercomparison, the testbed is applied to two models: the regionally-refined Simple Cloud-Resolving E3SM Atmosphere Model (SCREAM) at 6.5, 3.25 and 1.625 km grid spacing and the Weather Research and Forecasting (WRF) model with 3.2 and 1.6 km grid spacing. We find the simulation results to be highly sensitive to the initial conditions (ICs), initialization time, and model configurations, with ICs from the Rapid Refresh producing the best simulation. Significant improvement is identified in both models as horizontal grid spacing is refined. While a propagation delay of approximately 2 hr is found in both models, SCREAM at 1.625 km simulates the observed bow echo structure of the derecho well and predicts strong surface gusts that exceed 30 m/s. In comparison, WRF has difficulty producing surface wind over 25 m/s, with wind gusts in WRF 42%-46% lower than in SCREAM. However, WRF has a lower bias in simulating cloud top temperature and extent, but overestimates precipitation intensity. Both models reproduce the observed outgoing longwave radiation spatial patterns well (Pearson correlation >0.88), but, compared with NEXRAD observations, simulate generally larger areas of composite radar reflectivity >40 dBZ and underestimate the precipitating area by similar to 47%. Plain Language Summary This paper describes a testbed for evaluating model performance on a particular high-impact weather event-the June 2012 North American derecho, a storm event associated with extreme winds and precipitation. The testbed is applied to evaluate the Simple Cloud-Resolving E3SM Atmosphere Model (SCREAM) and the Weather Research and Forecasting (WRF) model at resolutions that resolve cloud systems. The performance of both models is shown to be sensitive to the data set used for model initialization. Finer grid resolution generally leads to better model performance. All simulations show a 2-hr delay in predicting the evolution of the derecho and produce more intense rainfall. SCREAM generates a more realistic convective front than WRF and produces stronger surface winds. The evaluation protocol can be used to better understand the credibility of model simulations of extreme events and guide model development.