Two-dimensional modeling and numerical analysis of a straight fin in a convective-radiative environment are presented. The energy equation is adapted to model a fin with rectangular profile in a flow field with streamwise variable heat transfer coefficient. The finite difference technique is used to discretize this equation and a numerical solution is obtained via an iterative scheme. Temperature profiles of the fin surface, fin efficiency and the heat dissipated per unit mass of the fin material are predicted at different flow velocities and thermal conditions. Also, a method is proposed to reduce the weight of the straight fin and in accordance to minimize the flow- pumping power by providing a nonuniform fin-height profile. This optimum profile is estimated by tracing the local effective fin heights that maximize the heat dissipated per unit mass. New correlations based on the predicted results are obtained for the fin effective height, fin efficiency and heat dissipated per unit mass as functions of the flow velocity, fin geometry, fin material-properties and the operating base temperature.