A simple model based on the Monin-Obukhov surface layer similarity theory of heat and momentum transport can be used to predict the latent heat flux for a variety of atmospheric and soil moisture conditions. Experiments were carried out on the Campbell Tract at the University of California, Davis, from 14 September to 23 November 1990. The latent heat flux was measured precisely with a large weighing lysimeter and the surface temperature by a thermal IR transducer. The evaporation predictions and lysimeter measurements overall were in good agreement (R2 = 0.86), including cases of dry surface conditions. Even low daily evaporation of the order of 1 mm could be modeled with the procedure studied.