I am called fog. I look like a pale, grey veil. I usually form when the wind is light and the air is damp. Sometimes I form because the ground cools enough to bring the air to its dew point, and the fog spreads slowly upward. That's when I'm called radiation fog. Fog often happens when the ground is very moist. I also form when a warm, moist wind blows over a cool surface. I am just like a cloud, except I am closer to the surface.