The first ingredient of a winter storm is the cold air. If you don't have cold air, your not going to get snow or ice. The next ingredient of a winter storm is moisture. When enough moisture forms in the lower and mid levels of the atmosphere, we then say that the atmosphere is "prime" for snowfall. The final mechanism of a winter storm is lift. We need something to raise the moist cool air at the surface and mid levels higher into the sky. When this air goes higher into the atmosphere, since the surrounding air is cooler, it condenses into a cloud and then falls as snow at the surface.