An assessment of waterspout occurrence in the Eastern Adriatic basin in 2010: Synoptic and mesoscale environment and forecasting method

In this paper we performed a comprehensive analysis of 19 waterspout events that occurred in the Eastern Adriatic basin in 2010. Data were collected from the synoptic and climatological weather stations and from eyewitness reports from newspapers and the internet. The geographical and temporal distributions of the waterspouts, as well as the absolute frequencies of four synoptic types relevant to waterspout development (south-west flow (SW), long-wave trough (LW), closed low (CLOSED) and short-wave trough (SWT)), are presented. The synoptic and mesoscale weather conditions were analyzed using the ERA-Interim reanalysis data, satellite images, data from synoptic and automatic weather stations and atmospheric soundings. To test waterspouts for thunderstorm relations the LINET network sensor data were used to infer lightning activity. Because thermodynamic instability indices are usually insufficient for forecasting waterspout activity, the performance of the Szilagyi Waterspout Nomogram (SWN) and the Szilagyi Waterspout Index (SWI) were tested using the ALADIN model. The results of the analyses of the 2010 cases show that the SWN successfully forecasted 15 out of 19 events (hit rate of 78.9%). This is a significant hit rate but is not as high as in the work of Keul et al. (2009), in which 96% of the Adriatic cases satisfied the nomogram. In addition, four selected waterspout cases, which represent the four basic synoptic types, were analyzed in detail to provide an overview of favorable atmospheric environments for waterspouts throughout the year.