The impact of planetary boundary layer (PBL) turbulence, land surface, and radiation parameterizations on mesoscale simulations of boundary layer properties in a coastal environment are examined using observations from different platforms and numerical simulations using the mesoscale model MM5 during a 10-day period in July 2004. The parameterization schemes examined are the MRF and Eta PBL schemes, the simple soil model and the more sophisticated NOAH land surface model, and the Dudhia and RRTM longwave radiation parameterizations. Comparisons are made between simulated and observed near surface mean variables, radiation, turbulence fluxes, mixed layer heights and morning inversion strengths, low-level jets, and land-sea breeze circulations. The comparisons indicate that for the Gulf Coast environment and typical summertime conditions, the Eta PBL scheme clearly outperforms the MRF PBL scheme in nearly all aspects. The results reveal that the popular Dudhia radiation scheme tends to overpredict the downward longwave radiation, which consequently results in a warm bias at night and a weaker nocturnal low level jet. Although the NOAH land surface model is much more sophisticated than the simple soil model, it failed to deliver significantly improved simulations of boundary layer properties for the conditions considered in this study.