A new index for high-impact weather forecasting is introduced and assessed in comparison with the well-established extreme forecast index (EFI). Two other ensemble summary statistics are also included in this comparison study: the shift-of-tail and a standardised ensemble mean anomaly. All these forecasts are based on the same ingredients: the ensemble forecast run at the European Centre for Medium-Range Weather Forecasts and the corresponding model climatology derived from a set of reforecasts. The new index emerges from recent developments in forecast verification of extreme events: it is derived as a consistent forecast with the diagonal score, a weighted version of the continuous ranked probability score targetting high-impact events. In this study, we emphasise the importance of forecast discretisation for communication purposes and decision-making. A forecast is actionable in the situation where a user can decide to take action when a threshold is exceeded by the forecast. Forecast verification is performed to assess both the potential skill of the different indices as well as their specific skill as actionable forecasts. Among the investigated actionable forecasts, the new proposed index demonstrates the strongest discrimination power, in particular at longer lead times, paving the way for seamless predictions of high-impact weather across time ranges.

翻译：本文引入并评估了一种新的高影响天气预报指数，并将其与公认的极端预报指数（EFI）进行比较。该对比研究还包含了另外两种集合汇总统计量：尾偏移量和标准化集合平均异常量。所有这些预报均基于相同的要素：欧洲中期天气预报中心运行的集合预报以及根据一组后报数据导出的相应模式气候态。新指数源于极端事件预报验证的最新进展：通过推导，它成为与对角线分数一致的预报，而后者是针对高影响事件的连续分级概率得分的加权版本。本研究强调了预报离散化在沟通和决策中的重要性。当用户能够根据预报超过阈值的情况决定采取行动时，该预报即为可行动预报。我们通过预报验证评估了各指数的潜在技能及其作为可行动预报的特定技能。在所研究的可行动预报中，新提出的指数表现出最强的区分能力，尤其是在较长预报时效下，这为跨时间范围的高影响天气事件的无缝预测铺平了道路。