In this study, a dense advection-radiation fog that occurred over the Grand Casablanca region, Morocco, during the night of 23–24 December 2013, is investigated. The adverse visibility induced by the fog patch led to a series of collisions and loss of life on a highway of the region. This fog event is simulated by the Meso-NH research model. Conventional observations from two synoptic stations, satellite imagery, and the European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis are used to analyze the physical processes during the whole life cycle of the event. Some hypotheses on the influence of environmental conditions (topography, land-sea heterogeneity, urbanization) on the numerical fog prediction are presented.