A computationally efficient three-equation model of the turbulent transport of momentum and heat for simulating a circulation structure over an areal heat source in a stable stratified environment is formulated and evaluated. Results of the numerical simulation demonstrate that the three-equation model is able to predict the circulation structure, which is in a good agreement with the experimental data. Effects of buoyancy on the mean temperature and vertical turbulent heat flux in the thermal stable stratified mixing layer behind a grid generating the turbulence have also been evaluated.