Analysis of a mesoscale convective system centred over the Río de la Plata

A mesoscale convective system developed over the Río de la Plata during the late evening of 30 May and the morning of 31 May 1985. This system produced very heavy precipitation and flash floods in metropolitan areas with a total accumulated precipitation maximising at 308.5 mm over Buenos Aires City, Argentina. The European Centre for Medium-Range Weather Forecasts (ECMWF) analyses reveal the presence of a low-level jet (LLJ) from the north-northwest with a core moving southeastward in the 850 hPa wind pattern and a short wave progressing from the west in the 500 hPa height fields. This LLJ contributed to the occurrence of a favourable mesoscale environment for the triggering of convection at its decelerating leading edge by enhancing the convergence of moisture flux at low levels. The evolutionary stages of the mesoscale system are described and a comparison is made between the environmental conditions during its life cycle and those found in a study by Maddox. Analysis of the divergence of the Q-vector field during the MCS mature stage shows that it develops in a weakly forced large scale environment.