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

A mesoscale convective system developed over the Rio de la Plata during the late evening of 30 May and the morning of 31 May 1985, This system produce d very heavy precipitation and flash floods in metropolitan areas with a to tal accumulated precipitation maximising at 308.5 mm over Buenos Aires City , Argentina. The European Centre for Medium-Range Weather Forecasts (ECMWF) analyses rev eal the presence of a low-level jet (LLJ) from the north-northwest with a c ore moving southeastward in the 850 hPa wind pattern and a short wave progr essing 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 compari son 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-vecto r field during the MCS mature stage shows that it develops in a weakly forc ed large scale environment.