Fog is the most important physical process that reduces surface visibility, having a major negative impact on air traffic. In this study, a one-dimensional boundary layer model was developed in order to predict the occurrence and intensity of fog. The model uses a selection of parameterisations, suggested by different authors, and uses the finite element method for the vertical discretisation of the equations. The 1977 Cabauw fog event is used to validate the model and eight fog events at Lisbon Airport are simulated. The validation shows that the model is able to predict realistically the fog's onset, growth and dissipation. The fog forecasts at Lisbon Airport are, in general, quite reasonable, and a simple simulation of a fog event, where advection played a fundamental role, also gives realistic results.