It has been recently shown for two forests in France (Les Landes and Sologne) that summer cloud cover over the forest is increased relative to its surroundings. This study aims to contribute to the elucidation of the physical mechanisms responsible for this increased cloud cover, focusing on surface flux partitioning. This was done by performing a case study for a heatwave day on which enhanced cloud cover over the forest of Les Landes was observed. Two numerical experiments (large‐eddy simulations) with a homogeneous forest cover were performed, one in which the sensible heat flux was increased by approximately 5% of the total available energy and another one in which the same amount of energy was added to the latent heat flux. The addition of energy to the sensible heat flux led to a stronger increase in cloud cover than the same addition to the latent heat flux. The mean relative humidity at the boundary layer top showed only small differences, indicating it was not a sufficient indicator for cloud formation in this case. Important information, which immediately underlines the need for large‐eddy simulations, is contained in modifications of the shape of the probability density functions of temperature and humidity. With enhanced sensible heating, the higher peak values of relative humidity contribute to an increased cloud cover. A crucial reason for the differences in cloud cover between the experiments is conjectured to be a decrease in the required amount of energy for air parcels to reach the lifting condensation level, indirectly caused by the boundary layer and near‐surface warming associated with the stronger sensible heat flux. As forests in the region do have a higher sensible heat flux than their surroundings, we highlight one potential mechanism for enhanced cloud cover. Cloud cover strongly depends on the distribution of the incoming solar and thermal energy between heating and evaporation, and therefore land use is crucial in determining cloud cover. We performed large‐eddy simulation experiments with various combinations of heating and evaporation. We found for our case study of a temperate forest that increases in the sensible heat flux are more important for cloud cover than increases in the latent heat flux, and have illustrated the mechanisms responsible for this.