Videosonde data from an Australian squall line were combined with a radar echo profile to construct a conceptual model of hydrometeor mass, number, and space charge evolution. Two-step hydrometeor growth modes were suggested: low-level, warm rain-frozen drop and high-level, graupel-ice crystals. A riming electrification mechanism successfully explained the charge distribution. A warm rain-frozen drop process was active in the forward area of the convective region, and frozen drop growth was highly active near the 0¿C level. Ice crystals, which electrified frozen drops positively, increased in number as they were lifted. Graupel growth was enhanced, and additional charge separation occurred between ice crystals and graupel in the upper level. Large negative graupel fell at the rear of the convective region, while positive ice crystals and small negative graupel were transported into the anvil. The reason for high lightning frequencies in a squall line over a maritime continent is also discussed.