The QUIC (Quick Urban & Industrial Complex) dispersion modeling system has been developed to provide high-resolution wind and concentration fields in cities. The fast response 3D urban wind model QUIC-URB explicitly solves for the flow field around buildings using a suite of empirical parameterizations and mass conservation. Previous evaluations of the model against single and multiple building wind tunnel data have shown weaknesses in several of the standard parameterizations. In particular, the upwind cavity associated with the horseshoe vortex does not compare well with experimental results. The cavity size is over predicted and the velocities within the cavity are quite poorly reproduced. In this work, the upwind cavity parameterization has been modified and evaluated against wind tunnel data for several rectangular building geometries. The upwind cavity has been divided into two regions: a displacement zone where a modified power law is implemented and a “front eddy” region where a simple vortex parameterization is specified. The models provide significant improvement over the previous standard parameterizations.