A thunderstorm which developed in North-Eastern region of Spain on 16th June, 2006 is analyzed. This thunderstorm could be severe because it produced hailstones larger than 19 mm. The cell life time was 3h 30 minutes. Radar cross-sections show a strong vertical development with cloud tops reaching an altitude of 13 km. During the first 3 h, in its mature stage, cloud-to-ground (CG) flash rates remained very low (under 1 min-1) with sometimes slightly dominant positive CG flashes. The maximum intra-cloud (IC) flash rate (67 min-1) peaked 24 minutes before the presence of reflectivity higher than 60 dBZ. During high reflectivity within the cloud the IC activity abruptly decreased. The maximum reflectivity observed by radar was consistent with the reported hail at ground.