The fog along the coast of the Golden Gate National Parks is called “advection fog.” This type of fog forms when humid air from the Pacific Ocean swoops over the chilly California wind current flowing parallel to the coast. The fog stays low to the ground and then the warm, moist air condenses as it moves across the San Francisco Bay or nearby land. This is common near any coastline. Fog is basically water droplets suspended in the air, mixed with dust and other microscopic particles. Typically, air already contains water vapor, and the warmer the air, the more H2O the air can hold. However, air can’t hold much water as it cools. When it reaches the dew point, it becomes fully saturated with water vapor. If the air cools even more, it loses the ability to hold all of that water vapor—forcing the vapor to condense around tiny, dust-sized particles to form droplets. When enough of these droplets accumulate—voila! Fog is born. Karl the Fog, is the name locals gave to this phenomenon.