United Parcel Service (UPS) Airlines has developed conceptual models and forecast methods for the prediction of radiation fog. A potential fog layer is viewed as being several hundred feet in vertical extent, and the importance of the vertical distribution of moisture (hydrolapse) in this layer is discussed. A technique for roughly inferring the hydrolapse in the absence of direct observations above shelter height is presented.

Mechanical turbulence and its effect on fog formation is discussed, and a technique for quantitatively forecasting turbulence using common forecast data and Richardson number concepts is presented. The importance of soil temperature and the consequent heat exchange between the lower atmosphere and the ground is discussed, as well as the potential for some pre-existing stratus cloud decks to "build down" to the surface as fog. The synoptic situation involving weak fronts with cloud cover clearing during the hours around sunset is highlighted as particularly prone to fog formation. Several case studies are presented to demonstrate the application of the UPS concepts and techniques.