Based on results from month-long mesoscale simulations using Mesoscale Model 5 (MM5) and observations for all of June 1996, the study has revealed the significance of diurnal variation of the characteristics of the marine atmospheric boundary layer (MABL) and cloudiness along the California coast. The authors found that wind components, wind divergence field, MABL depth, and supercriticality of the flow exhibit significant diurnal variation. The horizontal wind field structure over the inner 100 km is dominated by the response of the marine atmospheric boundary layer to land topography. Supercritical marine layer dynamics impose a compression bulge with convergent wind fields on the upwind side of major capes and an expansion fans with divergent wind fields on the downwind side. The area of the expansion fans is largest during daylight and the compression bulges are largest at night. In particular, this study focuses on investigation of wind stress and the curl of the wind stress as simulated by the model and computed from the spatially limited observations. The wind stress has a general structure similar to the winds, with greater stress in the expansion fans and less in the compression bulges. According to the analysis, the horizontal wind stress curl has systematic variation of the horizontal structure relative to the center of an expansion fan and compression bulge. The sign of the wind stress curl appears to be opposite on the coastal side of the center of these features as compared to the offshore region. The along- coast structure of the wind stress and wind stress curl has significant implications for coastal ocean upwelling, the biological response, and resource management.