The cloud fraction of shallow non-precipitating cumulus residing at the lifting condensation level increases in the afternoon, most evident in airborne lidar observations from EUREC4A. The EUREC4A/ATOMIC field campaign was a large international deployment that took place east of Barbados in January-February 2020. The cloudiness increase cannot be easily explained by afternoon increases in the ocean sea surface temperature. Observations from the German aircraft HALO platform and from the R/V Ronald H. Brown are used to investigate diurnal variations in sub-cloud boundary layer properties that might facilitate afternoon increases in the suppressed low-lying cloud population. The analysis benefits from the availability of many thermodynamic soundings combined with ship-board Doppler lidar and aircraft water vapor lidar data. We find a helpful weak afternoon increase in the near-surface specific humidity, and shortwave absorption further stratifies the lower one km during the afternoon, so that the clouds only remain while forced from above. Ongoing analysis, to be completed prior to the meeting, will explore if a diurnal cycle to the sub-cloud stratification is also present and how this relates to the vertical moisture distribution and inhibition by the transition layer between the sub-cloud and cloud layer.