FOG is usually late night/ early morning phenomenon when rapid cooling, high stability, light wind and need of low moisture for saturation dominates. Normally, it is believed that wind from water body brings moisture and facilitate fog formation. Practically, it does not happen as continuous blowing of warm air will keep the ground warm hampering the cooling process of night. During early morning hours, especially in winter land is quite cold in comparison to close by, river water/ ocean water. This sets in the land breeze circulation, that is, at ground wind blows from land to river/ocean and return counter current from river/ocean takes place at little elevated height within about 100m. This return current is highly moist and warm current as plenty of evaporation lakes place into the cold land breeze from warm river water. The counter current descends over land as warm moist air and comes into contact with cold land surface to get cooled giving rise to fog/mist formation. That is how counter current of land breeze becomes favourable for fog formation. Environment becomes more favourable if we have deep layer of moist air over the region, so that mixing from top does not dry up the lower levels.
Some of the location specific studies are presented here.