Diagnostic wind models provide mass-consistent wind velocity fields over complex orography on the basis of sparse measured data. For this purpose the model presented in this paper solves an elliptic differential equation to obtain wind fields satisfying the discrete formulation of the continuity equation. A proper parameterization accounts for the influence of atmospheric stability on the resulting wind fields. The solution procedure is based on the Conjugate Gradient Method and an efficient direct elliptic solver using FFT. Calculated mass-consistent wind fields in the Athens basin reveal the typical diurnal variation of sea breeze circulation. Detailed results allow a discussion of the major model features.