Quantitative comparison of METEOSAT thunderstorm detection and nowcasting with in situ reports in the European Severe Weather Database (ESWD)

Kurzfassung

Severe thunderstorms constitute a major weather hazard in Europe, with an estimated total damage of � 5-8 billion each year. Yet a pan-European database of severe weather reports in a homogeneous data format has become available only recently: the European Severe Weather Database (ESWD). We demonstrate the large potential of ESWD applications for storm detection and forecast evaluation purposes. The study of six warm-season severe weather days in Europe from 2007 and 2008 revealed that up to 47% of the ESWD reports were located exactly within the polygons detected by the Cb-TRAM algorithm for three different stages of deep moist convection. The cool-season case study of extratropical cyclone �Emma� on 1 March 2008 showed that low-topped winter thunderstorms provide a challenge for satellite storm detection and nowcasting adapted to warm-season storms with high, cold cloud tops. However, this case also demonstrated how ESWD reports alone can still be valuable to identify the hazardous regions along the cold front of the cyclone. The analysis of all warm-season (JJA) severe weather days in Europe in 2008 corroborated these findings. There is good agreement between ESWD reports and Cb-TRAM detected thunderstorms, even though no exact correspondence between ESWD reports and Cb-TRAM cells is required (e.g., due to storm morphology). Correspondingly, a large portion of ESWD reports regarded as misses by our strict in/out-of-Cb-TRAM-polygon criterion were still located close to a Cb-TRAM cell. Quantitatively, only the probability of detection (POD) can be evaluated due to the different characteristics of the two data sources. For the JJA 2008 period, the POD for storm detection was 0.24 on average, with maximum values up to 0.58. The respective analysis for the 30 and 60 minutes nowcasts yielded average POD values of 0.11 and 0.08, respectively, with maximum values of POD exceeding 0.4 on three different days for the 30 minutes nowcast and on one day for the 60 minutes nowcast.