In this study, a series of fog events that occurred near Halifax, Canada, during 20 June to 31 July 2016 are investigated using the Weather Research and Forecasting Model Version 3.8.1 (WRF), in comparison with in situ and satellite remotely sensed observations from the Moderate Resolution Imaging Spectroradiometer. We evaluate five planetary boundary layer (PBL) schemes available in WRF. Results show that these five PBL schemes lead to overestimates in liquid water content, especially the nonlocal schemes, and that they are biased early, in terms of the predicting the onset of fog, and late, in terms of fog dissipation, although their spatial patterns of fog are in good agreement with those suggested by Moderate Resolution Imaging Spectroradiometer imagery. The Kunkel equation is used to calculate visibility, based on WRF modeling of liquid water content. Comparisons with observed visibility show that this methodology sometimes fails to predict fog dissipation. We present a modification of this formulation for visibility that shows improved agreement with observations and more accurate fog dissipation. Continued improvements in the PBL scheme and visibility parameterization are needed for more accurate fog prediction.

Fog is defined to occur when the horizontal visibility decreases to <1 km because of a visible aerosol consisting of minute water droplets or ice crystals suspended in the air near the Earth's surface (Gultepe, 2008). Advection fog typically occurs when warm, moist air moves over the cold sea surface (Lewis et al., 2004). The Grand Banks of Newfoundland and waters off Atlantic Canada tend to be foggy because of the dominance of cold water from the Labrador Current, which flows from the Arctic Ocean, south along the coast of Labrador and passes around Newfoundland, continuing south along the East Coast of Canada near Nova Scotia, collocated with southerly winds caused by the North Atlantic High (NAH). These characteristics make the Grand Banks one of the foggiest places in the world (Koračin & Dorman, 2017), with a variety of different fog types, which can make fog studies challenging. Accurate simulations and forecasts of marine fog are important for these waters off Canada's East Coast, because of societal interest in this area, such as marine transport, offshore oil and gas activities, fisheries, recreational boating, search and rescue, and national security.Like fog, stratus is also a concern to many societal activities, for example, its influence on aviation security. Because stratus also contributes to the radiation budget, it is important to investigate its formation. Wylie et al. (1989) studied low-cloud characteristics during the first International Satellite Cloud Climatological Project (ISCCP) Regional Experiment. Their results showed that cold advection in the planetary boundary layer (PBL) plays an important role in increasing the formation of low-cloud events. Furthermore,