The representation of the PBL clouds in the NWP and climate models is a subject of permanent discussion, due to the importance of these phenomena in the radiative budget of the atmosphere and in the transport of energy and matter between the earth's surface and the free atmosphere.

In this work we present the results of two SCM diurnal cycle simulations of typical boundary layer clouds (stratocumulus and shallow cumulus). First a 37-hour run (almost a two day's cycle) of a marine Sc, with data out of the FIRE campaign. The evolution of the cloud compares well with the LES reference simulations. Second a 14-hour run of cumulus over land, from the ARM data base. Here the main challenge is to capture the set up of the cloudy layer and the time of its disappearance -which is well captured by the simulation-, as well as the proper mean cloud cover and liquid water contents -overestimated.

The simulations are performed using only a moist TKE-based turbulence scheme (no convection or microphysics schemes activated), and the main new feature is the use of a single mixing length formulation apt for both cases as well as for dry PBL simulations. This length is physically based on buoyancy considerations.