Abstract: A good number of Grid middlewares have been developed recently, yet their effective use for real world applications is seldom validated. Meanwhile, high-performance computing codes keep on requiring more resources than even large clusters can deliver. In this paper, the G-BRAMS project is presented, which aims at executing climatology simulations on a three tiers grid. Three different middlewares (Globus, OAR/CIGRI and OurGrid) are compared and some preliminary measurements are presented. The outcome will be the definition of a Computational Grid, adapted to run a mesoscale meteorological model (BRAMS) used in weather and climatology forecasting that may demand several hundreds of independent executions, one for each different initial condition. The proposed grid is employed to perform these executions for a given middleware. Each execution is scheduled as an MPI job in a particular cluster that is part of the grid.