A thermal bar is defined here as a zone of descending water at or near the fresh water temperature of maximum density. In the present study, we model physical properties such as velocity, temperature, turbulent fluxes, time of onset, and migration speed of the thermal bar in an idealized basin. Unlike models using prescribed eddy viscosity and diffusivity coefficients, our model uses a second-order turbulence closure scheme to model mixing due to turbulence. The only inputs in the calculation are the surface wind, the surface heat flux, and the initial state of the fluid. Numerical simulations of the resulting circulation are presented for flow in a long rotating basin under prescribed surface heat and wind conditions. The results show the influence of the relative magnitudes of mechanical and thermal forcing on the circulation. A comparison with field observations shows reasonable agreement between computed and measured bar migration speeds. The time necessary for the formation of the bar is computed, and is found to depend on the surface forcing. ¿ 1998 American Geophysical Union