A simulation tool has been developed to simulate the wind fields, turbulence fields, and the unsteady dispersion of NCBR substances in urban areas on the building to city blocks scale. This Computational Fluid Dynamics (CFD)-based approach has been shown to accurately simulate the urban wind and turbulence fields with minimal approximations, and has been demonstrated by modeling the flow fields and simulated release of CBW agent near the White House and in a region of Salt Lake City. This Urban Dispersion Simulator (UDS) utilizes recent advances in modern CFD algorithms, uses an automated model setup via a unique image-based approach, and is driven by an intuitive interface. This paper outlines the modeling approaches taken, including both CFD and solid model generation, and shows results comparing computed and experimental data for the flow over obstacle arrays simulating the urban environment. Results from the dispersion simulation demonstrations are shown for release near the White House using realistic geometric models.