Mesoscale circulations generated by landscape discontinuities (e.g., sea breezes) are likely to have a significant impact on the hydrologic cycle, the climate, and the weather. However, these processes are not represented in large-scale atmospheric models (e.g., general circulation models), which have an inappropriate grid-scale resolution. With the assumption that atmospheric variables can be separated into large scale, mesoscale, and turbulent scale, a set of prognostic equations applicable in large-scale atmospheric models for momentum, temperature, moisture, and any other gaseous or aerosol material, which includes both mesoscale and turbulent fluxes is developed. Prognostic equations are also developed for these mesoscale fluxes, which indicate a closure problem and, therefore, require a parameterization. For this purpose, the mean mesoscale kinetic energy (MKE) per unit of mass is used, defined as Ẽ = 0.5 〈ui′2〉 where ui′ represents the three Cartesian components of a mesoscale circulation ... Abstract Mesoscale circulations generated by landscape discontinuities (e.g., sea breezes) are likely to have a significant impact on the hydrologic cycle, the climate, and the weather. However, these processes are not represented in large-scale atmospheric models (e.g., general circulation models), which have an inappropriate grid-scale resolution. With the assumption that atmospheric variables can be separated into large scale, mesoscale, and turbulent scale, a set of prognostic equations applicable in large-scale atmospheric models for momentum, temperature, moisture, and any other gaseous or aerosol material, which includes both mesoscale and turbulent fluxes is developed. Prognostic equations are also developed for these mesoscale fluxes, which indicate a closure problem and, therefore, require a parameterization. For this purpose, the mean mesoscale kinetic energy (MKE) per unit of mass is used, defined as Ẽ = 0.5 〈ui′2〉 where ui′ represents the three Cartesian components of a mesoscale circulation ...