Whether it softly comes in on little cat feet, or rolls in like a spooky movie, everyone has experienced fog. Although there are different types of fog, essentially fog is a cloud on the ground which reduces visibility to less than 1km. The basic requirements for fog to form are moisture in the air – the closer to 100% humidity the better, and the air near the ground must be cooling to within 5 F (3 C) of dew point – this is the temperature to which air must be cooled in order for water vapor in the air to condense to liquid water. When the air near the ground cools to dew point, the water vapor in the air will become visible as fog in the air or dew on the ground. Draw on your screen.