The regional Eta/CPTEC model has been producing operationally forecasts over South America since 1996. The objective of this work is to evaluate the model predictions during strong meridional mass exchange over South America based on different model domain and grid-size configurations. Six cases of cold air intrusion and eight examples of warm air intrusion associated to convective activity over middle latitudes were chosen for the study. The model was evaluated against the NCEP global analyses, based on statistical verification parameters. Global analyses were interpolated bilinearly to the 40-km Eta model output grid. Larger forecasts errors were found close to the southern boundary of the domain in both cold and warm air cases. These errors suggest the presence of strong forcing near the southern boundary generating errors which propagate toward the interior of the domain. The substitution of the boundary conditions to analyses reduced substantially the errors in the interior. The unavailability of regional analyses limited the study. However the conclusion of large forecast errors being generated at the southern boundaries is apparent, and an increase in model domain is recommended for the 40-km version