Deep convection occurs periodically in the Gulf of Lion, driven by the seasonal atmospheric change and Mistral winds. To determine the variability and drivers of the seasonal and Mistral forcing, 20 years of ocean simulations were run. Two sets of simulations were performed: a control set, forced by unfiltered atmospheric forcing, and a seasonal set, forced by filtered forcing. The filtered forcing retained the seasonal aspects but removed the high frequency phenomena. Assuming the Mistral acts primarily in the high frequency, comparing the two sets allows for distinguishing the effects of the Mistral on the ocean response. During the preconditioning phase, the seasonal forcing was found to be the main destratifying process, removing on average 45.7% of the stratification, versus the 28.0% removed by the Mistral. Despite this difference, at the time of deep convection, both the seasonal and Mistral forcing each triggered deep convection in roughly half of the events. Larger sensible and latent heat fluxes were found in the seasonal forcing of the years with deep convection, acting as the main drivers (removing 0.17 m2s-2 and 0.43 m2s-2 of stratification, respectively). They are themselves driven by increased wind speeds, believed to be the low frequency signal of the Mistral, as more Mistral events occur during winters with deep convection (34.3% versus 28.6%). The evolution of the seasonal forcing in a changing climate may have a significant effect on the future deep convection cycle of the Gulf of Lion.