The Operational Program on the Exchange of Weather Radar Information (OPERA) has co-ordinated radar co-operation among national weather services in Europe for more than 20 years. It has introduced its own, manufacturer-independent data model, runs its own data center, and produces Pan-European radar composites. The applications using this data vary from data assimilation to flood warnings and the monitoring of animal migration. It has used several approaches to provide a homogeneous combination of disparate raw data and to indicate the reliability of its products. In particular, if a pixel shows no precipitation, it is important to know if that pixel is dry or if the measurement was missing.

The goal of the present study was to exploit the volumetric data from the Wideumont weather radar to estimate the occurrence and severity of hail over a period of 10 years (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012). The radar is located in the southeastern part of Belgium and its domain covers Belgium, Luxembourg and some parts of Germany, France and The Netherlands. Two hail detection algorithms were used for detecting hail falls in the volumetric radar data. The algorithms provide an empirical estimation of the probability of hail (POH) and the probability of severe hail (POSH). The study shows that post-processing of probabilities by means of the advection correction significantly influences the statistical results about hail occurrence. The advection correction is very effective in reducing the 'fishbone effect' due to a temporal sampling of the radar data that is too low, which has an impact on the geographical distribution of the hail fall frequencies over the study domain. The post-processed POH and POSH datasets are verified against hail reports at the ground. The statistics obtained show that the diurnal cycle of hail falls has a pronounced peak in the 1500-1600 UTC (local solar time + 1 h) time interval with 28% of all hail events occurring in July and 30% of severe hail events occurring in May. Nevertheless, severe hail events have a low occurrence in absolute terms and longer time series of observations are required to obtain a more reliable severe hail climatology.

Large parts of the continents are continuously scanned by terrestrial weather radars to monitor precipitation and wind conditions. These systems also monitor the mass movements of bird, bat, and insect migration, but it is still unknown how many of these systems perform with regard to detection and quantification of migration intensities of the different groups. In this study that was undertaken within five regions across Europe and the Middle East we examined to what extent bird migration intensities derived from different weather radars are comparable between each other and relate to intensities measured by local small‐scaled radars, some of them specifically developed to monitor birds. Good correspondence was found for the relative day‐to‐day pattern in migration intensities among most radar systems that were compared. Absolute intensities varied between different systems and regions. The findings of this study can be used to infer about absolute bird migration intensities measured by different radar systems and consequently help resolving methodological issues regarding the estimation of migrant numbers in the Western‐Palearctic region. It further depicts a scientific basis for the future monitoring of migratory bird populations across a large spatio‐temporal scale, predicting their movements and studying its consequences on ecological systems and human lives.