We present an investigation into the planetary boundary layer (PBL) parameterization processes that contributed to the success or failure of the Unified Forecast System (UFS) to simulate a case in which coastal New England was impacted by fog. In the regional version of the UFS known as the Short-Range Weather Application (SRWapp), two different physics configurations were applied. Only one of these configurations was able to successfully simulate the fog event. Subsequent tests using the single-column version of the model (SCM) focus on parameterized physical processes in the two PBL schemes used, to explore the impact of some differences between the schemes as they contribute to the formation of fog in this case. This work highlights the uncertainty of some assumptions used in these PBL parameterizations, with particular focus on diffusion and transport processes near the surface.