The data from surface automatic weather stations show that in the area of the Llobregat delta (northeast of the Iberian Peninsula) we can observe greater precipitation than in nearby inland areas (Ordal, Collserola, Garraf), than on the other side of a massif located on the coast (Garraf) and than on the northern coast. This distribution of the precipitation could be explained by the formation of a nocturnal surface cold front in the Llobregat delta. In order to analyze in-depth the physical mechanisms that can influence the formation of this front (topography, sea and drainage winds), two rain episodes in the area were simulated with the MM5 mesoscale model, reproducing satisfactorily the physical mechanisms that favor the appearance of the front.