Synoptic and mesoscale aspects related to the formation of a mesoscale convective system (MCS), which affected Paraguay on 3 February 2001, are analyzed. The MCS has its origin between 18:00 and 21:00 GMT on the 2nd of February on the southeastern part of Bolivia, affecting afterwards the northern part of Argentina and the central and southern regions of Paraguay. The MCS produced intense rains over the Paraguayan territory, specially in the central part of the Región Oriental, where 69 mm fell in two hours at Villarrica. The rainfall type over the Paraguayan territory was mostly of convective origin. The severe convective processes had their origin at the time of maximum solar heating in the area, where low pressures at lower layers and an anti-cyclone at the top of the troposphere were predominating. The principal factors on the synoptic scale and the mesoscale, which generated the MCS, were: (1) The presence of a Low Level Jet from which the MCS originated, which was generating a cyclonic horizontal shear over the area; (2) the formation of strong convergence associated with diurnal heating and a low pressure system at the surface in the area where the MCS generated; (3) the presence of humid air advected by the Low Level Jet, showed by dew point temperatures greater than 22 °C in the area of development of the MCS; and (4) the predominance, at the birth of the system, of a pre-existing very divergent anti-cyclonic system at the upper troposphere, which was intensified by the own evolution of the MCS.
