Radiation fog prediction using a simple numerical model

A simple one-dimensional numerical-analytical model was developed by MEYER and RAO (1995) to predict the onset of radiation fog. The model computes ra diative cooling and turbulent diffusion of heat and vapor through the lower boundary layer and produces heat and vapor fluxes at the soil-atmosphere i nterface. The model is designed for Air Force forecasters a,ho have access to a personal computer, an early evening surface observation of the dry bul b and dewpoint temperature, wind speed, the lapse rate in the upper boundar y layer, and the previous 24-h precipitation amount. These initial data are used to predict the diurnal variation of the dry bulb and dewpoint tempera tures at 10 m above the surface. In accordance with conventional synoptic o bserving practices, fog is defined as a restriction of the surface visibili ty generally to less than 1000 m. Fog is assumed to occur in the model pred ictions when the dewpoint depression falls to less than 1 degrees C. Observ ations, from several Air Force bases for selected days when fog was observe d to occur, were used to test the model. The present model with default par ameters appears to predict the onset of fog slightly ahead of its occurrenc e. Better verification results are expected when site-relevant parameters a re used in model predictions.