As a severe weather phenomenon, thunderstorms can cause casualties and economic loss to the human society. A reliable forecast of these weather events would help to avoid or at least mitigate this damage. To date, the forecasting of thunderstorms however is still a challenge, especially for lead times of one hour and beyond. In this study we present a methodology to forecast deep-convection for several hours lead time: Cb‑Fusion. Cb‑Fusion estimates the likelihood of thunderstorm occurrence for up to 6 hours in advance over a part of Central Europe, using a data fusion technique that blends data of multiple sources from observations, nowcasts, and numerical weather predictions with a high update rate. The Cb‑Fusion is set up to operate in near real time. The skill of Cb‑Fusion is evaluated based on 1743 hours of thunderstorm observations collected during the months April to October, 2019. Three categories of thunderstorm size have been distinguished: ‘large’ for a coverage area larger than 5000 km2, ‘medium’ for a coverage area between 5000 km2 and 500 km2, and ‘small’ for a coverage area smaller than 500 km2. Compared to thunderstorm forecasts from numerical models alone, the combination of data from various sources by Cb‑Fusion results in a significantly better forecast skill. The study reveals that the forecast is reliable for up to 3 hours lead time for ‘medium’ and ‘large’ scale thunderstorms (median POD of 0.6–0.9) but little skill is found for ‘small’ scale thunderstorms and lead times between 3 and 6 hours (median POD of 0.05). It is argued that Cb‑Fusion provides meaningful improvements in forecasting thunderstorms for various users.

中文翻译：

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Cb‑Fusion –预测长达6小时的雷暴雨单元

雷暴是一种严重的天气现象，可能给人类社会造成人员伤亡和经济损失。对这些天气事件的可靠预测将有助于避免或至少减轻这种破坏。迄今为止，对雷暴的预报仍然是一个挑战，特别是对于一小时或更长时间的交货时间。在这项研究中，我们提出了一种预测交货时间为数小时的深对流的方法：Cb‑Fusion。Cb-Fusion使用数据融合技术，以高更新率将来自观测，临近预报和数值天气预报的多种来源的数据融合在一起，从而在中欧部分地区提前估计了长达6小时的雷暴发生的可能性。Cb‑Fusion设置为几乎实时运行。根据在2019年4月至2019年10月期间收集的1743个小时雷暴观测资料，评估了Cb‑Fusion的技能。区分了三类雷暴大小：覆盖范围大于5000 km2的“大”，“覆盖范围”的“中”。覆盖面积介于5000 km2和500 km2之间，“较小”表示覆盖面积小于500 km2。与仅通过数值模型进行的雷暴预报相比，Cb‑Fusion将来自各种来源的数据进行组合可以显着提高预报技巧。研究表明，对于“中型”和“大型”雷暴（中位数POD为0.6-0.9），预报在长达3个小时的提前时间内是可靠的，但对于“小型”雷暴和3至2的提前期，预报技巧很少。 6小时（平均POD为0.05）。