During the warm months of the year in Catalonia, the marine air overcomes the coastal mountain range and reaches the eastern Ebro sub-basin. This phenomenon is called marinada and has recently been thoroughly characterized for the first time by Jiménez et al. (2023), based on surface climatological data. However, the main physical mechanisms involved in its arrival and propagation remain to be discovered. This study aims to understand how the marinada is formed and how it interacts with the already developed atmospheric boundary layer. Surface and atmospheric observations are used in combination with the coupled surface–atmosphere model Meso-NH to reveal the mechanisms at play. It is shown that the marinada is generated by the advection of a cool marine air mass over the Catalan Pre-coastal Range by the action of the sea breeze and the upslope wind. This marine air mass then flows into the Ebro basin, creating what is known as the marinada. The characteristics and dynamics of the marinada allow it to be classified as a fall wind. It is also shown that the arrival, propagation and decay of the marinada is strongly dependent on the larger-scale weather situation: westerlies or thermal low. The current study provides a consistent framework for understanding the marinada, paving the way for better modeling and prediction of the phenomenon.