Deep convection east of the Andes Cordillera: Four hailstorm cases

An analysis of four cases of severe hailstorms that occurred east of the Andes Cordillera in the northern part of Argentina is presented in this article. Analysed and observed data, as well as mesoscale model integrations, are used to evidentiate the underlying physical mechanism. The formation of heavy hailstones is the consequence of intense deep moist convection, with sufficiently high updraft speed to produce super-cooled water. The presence of warm and moist air is found. It appears to be a necessary but not sufficient condition to generate such intense convection. Convergence of moist enthalpy near the ground is also found. The passage of a cold front creates instabilities and causes upward motion on the warm side of the front, facilitating the development of deep convection. In some cases, low-level flow around a mountain creates wind convergence on the lee side, associated with lifting of air parcels. Although mountain waves are very frequent in the region, they do not appear determinant for the triggering of convection in the cases studied. It must be stressed that the results of this study are the consequences of the climatology of the region and cannot be trivially extrapolated to other regions.