Contemporary Earth system models mostly ignore the sub-grid scale (SGS) heterogeneous coupling between the land surface and atmosphere, to a detriment that remains largely unknown. To both evaluate the effect of SGS heterogeneity for realistic scenarios and aid in the development of coupled land and atmosphere SGS parameterizations for global models, we present a study of the effect of sub-100 km scale land-surface heterogeneity on cloud development. In the primary experiment we use the Weather Research and Forecasting (WRF) model to conduct two large-eddy simulations over the Southern Great Plains (SGP) site using 100-m horizontal resolution on a domain that spans 100 km in each lateral direction. The first simulation uses high-resolution land-surface fields specified by an offline land-surface model (LSM), while the second uses homogenized land-surface fields found by taking a domain-averaged value of each field at each timestep. The atmospheric development of the heterogeneous and homogeneous simulations are compared, primarily in terms of cloud production and turbulent kinetic energy. It is seen that the heterogeneous case develops a mesoscale circulation pattern which generates additional clouds and turbulence compared to the homogeneous case. Additional experiments isolate sources of heterogeneity in the LSM (including forcing meteorology) to better understand relevant land-surface processes, and modify the Bowen ratio and initial wind profile of the heterogeneous case to clarify the results seen. Finally two additional days at the SGP site are simulated confirming the increase in cloud production in heterogeneous cases.