This article describes the enablement of the MM5 Meteorological model as a Computational Grid Workflow. Considering the challenges involved in converting legacy high performance scientific applications as service based workflows, this article provides an in-depth analysis and solutions thereof to design a Grid service based workflow of HPC scientific applications. It also captures the need and design of scientific workflows based on re-usable components and services. A brief overview of the performance parameters for this grid workflow is also included. Further this article is also intended to serve as a reference document for enthusiasts to grid enable other legacy applications in various areas such as Seismic research, Oil exploration, and other advanced industrial and business applications.