Thunderstorms followed by flash flood events are recurrent in the Metropolitan Area of São Paulo during the wet seasons. The performance of several numerical simulations of the February 04, 2004 event carried out with the ARPS system in high horizontal resolution is evaluated through statistical errors and indices of accuracy. The evaluation is based on direct confrontation of the accumulated precipitation fields simulated by the model and measured by the São Paulo weather radar. The results quantify the influence of the advective terms of the primitive equations on phase errors of the simulated convective systems. The incremental assimilation of surface station data done during the model execution improved its performance in the area limited by the influence radius, which is defined during the objective analysis process. A new skill index formulation is presented (D PIELKE). The preliminary results indicate that the D PIELKE index is adequate for assessing the simulation skill of small-scale convective systems.
thunderstorms; mesoscale numerical simulations; phase and amplitude errors; indices of accuracy
