Documentation during January and February 2000 of the structure of severe convective storms in Mendoza, Argentina, with a cloud-physics jet aircraft penetrating the major feeder clouds from cloud base to the −45°C isotherm level is reported. Complementary radar, satellite, and radiosonde measurements are incorporated into the study. The main research goal was the description of the microphysical evolution of the convective feeders of the hailstorms from cloud base to the anvil in an attempt to gain insights into the microphysical evolution of the clouds that are associated with the high frequency of large hail in the region. The aircraft penetrated preferentially the tops of young growing elements, which were typically the major feeders to severe hailstorms, producing hail that is large (>3 cm) in size. Cloud bases typically were at 6°–14°C, with typical base updrafts of 4–7 m s−1. The cloud updrafts increased with height, exceeding 25 m s−1 at heights ≥7 km and, on occasion, 40 m s−1 at heights >8 km. Thermal buoyancies of 5°–8°C were measured in the convective towers at heights of 8–10 km. The vertical wind shear was weak below 6 km but increased strongly above that level as the west winds cleared the Andes barrier, which averages 6.1 km to the west of Mendoza. The clouds had very little coalescence and contained no detectable precipitation-sized particles >100 μm at temperatures >−15°C. Nearly adiabatic cloud water with most cloud water still not converted into precipitation-sized hydrometeors (>100 μm in diameter) was found in cloud filaments within the strongest updrafts up to the level of homogeneous freezing, reaching 4 g m−3 at −38°C in one cloud before vanishing abruptly at colder temperatures. Graupel >1 mm appeared at the tops of growing new towers at temperatures <−27°C, in agreement with radar first-echo heights of about 8 km.