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In coastal California, the principal source of Numerical Weather Prediction (NWP) model inaccuracy in the solar irradiance at the surface is the presence of marine layer stratocumulus clouds (MLS). The effect of several combinations of cloud microphysics, cumulus, radiation, and planetary boundary layer parameterization schemes on simulating marine stratocumulus clouds is examined in the Weather Research and Forecasting Model (WRF). Additionally, a reduced physical parameterization ensemble is created by means of an objective classification method. The overall ensemble downwelling shortwave is biased by 46 W m-2 in daytime, on average. The most important parameterization generating variability in downwelling shortwave is the cumulus scheme followed by the radiation scheme. However, the microphysics option has a strong influence for the cloudier cases. During persistent MLS cover days, the cloud cover duration is generally underestimated while during the limited MLS cover days, the models overpredict cloud cover duration. All configurations generally tend to overestimate morning solar irradiance indicating that MLS are not properly represented in this critical period. Keywords-solar forecast, numerical weather prediction, stratocumulus, ensemble forecasting. [ABSTRACT FROM AUTHOR]