The phenomenon involved in a lawn grass becoming wet in the morning during winter is called condensation. During early winter mornings, the temperature is low, which means that the air is cool. Due to the cold climate, the water vapor present in the atmosphere condenses to form dew drops on the grass blades. Dew is liquid water droplets that form on grass, spider webs, and other things in the early morning or late evening. Water molecules in the air continually bombard surfaces, like blades of grass, and some of the molecules stick, forming a very thin film of water. This happens because the ground outside cools down by radiating or emitting its heat, and at a certain point, water vapor in the air will begin to condense faster than water is evaporating, forming dew on surfaces that arent warmed by the heat radiated from the ground.