Four years (2011–2014) of the summer period (May–September) dual‐polarization Doppler C‐band weather radar data for Sürgavere, Estonia, were examined to determine the best indicator for cloud‐to‐ground lightning activity. Furthermore, the legacy radar‐derived hail indicator probability of hail and the storm maximum reflectivity were compared with the polarimetric hydrometeor classification algorithm (HCA) to establish a link between them and ensure data continuity. The study is based on convective storm cells identified from radar reflectivity data, using a 35 dBZ reflectivity threshold. Applying this threshold to the radar data resulted in 123 360 individual storm cells. It was found that 33.9% of the identified cells produced lightning and 25.9% hail. The number of individual storm cells on average is highest in the afternoon at 1600 local time and the mean storm cell area is largest in the evening at 2100 local time. Echo top 15 dBZ (ET15), ET20 and ET25 achieved the highest scores in terms of critical success index (0.39, 0.39 and 0.38 respectively), Heidke skill score (0.24, 0.26, 0.27) and equitable threat score (0.14, 0.15, 0.16). The graupel class of the dual‐polarization radar hydrometeor classification showed a similar performance to the 35 dBZ echo top. It was also shown that the reflectivity value just below 50 dBZ indicates the best skill for detection of hail, if HCA hail detection is used as the ground truth. The probability of hail value that shows the best agreement with the HCA hail class is 0.2.

Abstract. Accurate, timely, and reliable precipitation observations are mandatory for hydrological forecast and early warning systems. In the case of convective precipitation, traditional rain gauge networks often miss precipitation maxima, due to density limitations and the high spatial variability of the rainfall field. Despite several limitations like attenuation or partial beam blocking, the use of C-band weather radar has become operational in most European weather services. Traditionally, weather-radar-based quantitative precipitation estimation (QPE) is derived from horizontal reflectivity data. Nevertheless, dual-polarization weather radar can overcome several shortcomings of the conventional horizontal-reflectivity-based estimation. As weather radar archives are growing, they are becoming increasingly important for climatological purposes in addition to operational use. For the first time, the present study analyses one of the longest datasets from fully operational polarimetric C-band weather radars; these are located in Estonia and Italy, in very different climate conditions and environments. The length of the datasets used in the study is 5 years for both Estonia and Italy. The study focuses on long-term observations of summertime precipitation and their quantitative estimations by polarimetric observations. From such derived QPEs, accumulations for 1 h, 24 h, and 1-month durations are calculated and compared with reference rain gauges to quantify uncertainties and evaluate performances. Overall, the radar products showed similar results in Estonia and Italy when compared to each other. The product where radar reflectivity and specific differential phase were combined based on a threshold exhibited the best agreement with gauge values in all accumulation periods. In both countries reflectivity-based rainfall QPE underestimated and specific differential-phase-based product overestimated gauge measurements.

Abstract. Accurate, timely and reliable precipitation observations are mandatory for hydrological forecast and early warning systems. In the case of convective precipitations, traditional rain gauges networks often miss precipitation maxima, due to density limitations and high spatial variability of rainfall field. Despite several limitations like attenuation or partial beam-blockings, the use of C-band weather radar has become operational in most of European weather services. Traditionally, weather radar-based quantitative precipitation estimation (QPE) are derived by horizontal reflectivity data. Nevertheless, dual-polarization weather radar can overcome a number of shortcomings of the legacy horizontal reflectivity based estimation. For the first time, the present study analyses one of the longest datasets from fully operational polarimetric C-band weather radars; those ones are located in Estonia and in Italy, in very different climate conditions and environments. The study focuses on long-term observations of summertime precipitation and their quantitative estimations by polarimetric observations. From such derived QPEs accumulations for 1 hour, 24 hours and one month durations are calculated and compared with reference rain gauges to quantify uncertainties and evaluate performances.