Cold on the water: mechanisms, impacts, and future scenarios of lake-effect snowfall in Italy and Japan

Lake-effect snowfall was largely studied around the North American Great Lakes, yet similar processes arise in other coastal and mountainous regions where cold continental air flows over comparatively warm water. In this study, we investigate lake-effect snow in two seemingly distant but meteorologically comparable settings: the central Apennines in Italy, influenced by the Adriatic Sea, and Japan’s Niigata Prefecture, affected by air masses crossing the Sea of Japan. Despite their geographical distance, both regions share key ingredients: shallow and narrow seas acting as efficient heat and moisture sources, strong cold-air spells, and steep orography that enhances convergence and precipitation. This results in remarkably analogous snowfall extremes, which are both a key water resource and an intense hazard. Using ground-based observations, weather radar data, and future climate projections, we characterized the mechanisms driving these events and assessed their local impacts, including road closures, infrastructure disruptions, and structural failures. Particular attention was given to how warming air masses and concurrently warming sea surfaces may alter the frequency, intensity, and spatial distribution of lake-effect episodes. Our findings indicate that these phenomena represent a significant and often underestimated hazard, and that their sensitivity to climatic shifts exposes both regions to growing vulnerabilities in a warming world.