An Assessment of Ensemble Forecast Performance: Where We Are and Where We Should Go?

NWS has been entering a new era called “Probabilistic Impact-Based Decision Support Services” (Probabilistic IDSS). The key supporting backbone of this new Probabilistic IDSS capability is the operational ensemble prediction systems (EPSs) from the national centers. However, the development of ensemble forecasting techniques has been stagnant in recent years after a period of rapid development. Therefore, it is time and necessary to assess the status of current operational ensemble forecasts’ performances before we can further develop EPSs with clearer objectives such as where to improve and what to develop. This work examines the various building blocks of an ensemble forecast such as unperturbed member (control) vs. perturbed members, control member vs. ensemble mean, ensemble spread and its growth related to atmospheric instabilities, and forecast information contained in an ensemble cloud (such as the best and worst members and performance ranking of members). Suggestions on path forward about operational EPS development will be discussed based on the investigation results.