The simple answer to why Buffalo receives so much snow, and why it is is often confined to a specific area, is lake effect snow. Lake effect snow occurs most frequently during cold snaps in early winter. It happens when the transfer of heat and moisture from the warm waters of the Great Lakes to the cold air creates a shallow layer of atmospheric instability, causing air to rise quickly. As the moisture rises and condenses, it begins to fall as snow–and often, a lot of snow. Depending on which direction the winds are blowing, areas in the snow belts near the Great Lakes (including Buffalo) can see several feet of snow in just a few days. According to the National Weather Service, in the Buffalo area, when cold air from Canada moves over the still unfrozen, relatively warm Great Lakes, the lake moisture and instability from this temperature contrast build one or more bands of snow. These bands are then deposited over locations downwind from the lakes, with some areas receiving much more snow than others, depending on their location and the wind direction.