Methods to evaluate probabilistic and ensemble forecasts

Yuejian Zhu and Zoltan Toth


The introduction of probabilistic weather, water, and climate forecasts is one of the strategic goals of the NWS. Ensemble forecasting offers a practical tool to generate objective guidance for the issuance of such forecasts. The verification of probabilistic and ensemble forecasts requires methods different from those used to evaluate single value or categorical forecasts. This presentation will review the main attributes of probabilistic forecasts, resolution and reliability. Different verification scores, such as the Brier Skill Score, Ranked Probability Skill Score, the Relative Operating Charactersitics, etc. will be introduced and evaluated as to how they measure the main attributes of forecasts. In addition, the relationship between verification and statistical postprocessing of probabilistic forecasts will also be discussed.