The structure of a bow-echo system that crossed southeast France on 24 September 2012 during the first Special Observation Period of the Hydrological cycle in the Mediterranean Experiment (HyMeX) is investigated from a three-dimensional lightning mapping array (LMA), an operational lightning network, and operational polarimetric radar observations. Lightning observations reveal that 97% of flash initiation and 93% of flash propagation occurred within the convective region. Through combining LMA and radar-derived microphysical data it is also shown that lightning initiation events and propagation mostly occurred in regions containing graupel (initiation = 70%, propagation = 58%), ice (initiation = 22%, propagation = 33%), and to a lesser extent hail (initiation = 6%, propagation = 5%). The detailed analysis of the lightning activity during two periods of contrasted electrical activity suggests that wet hail growth processes and/or charge redistribution within the cloud may have had a negative impact on lightning initiation occurrences and propagation. The most active periods in terms of lightning activity occurred in conjunction with a vigorous, terrain driven, updraught that transported graupel particles above a height of 12 km.