Weather Whys; Fog Types

This is weather-wise. The fog begins when water vapor condenses onto tiny particles in the atmosphere. Gradually, those droplets become large enough to be seen. They form a haze, and if the haze thickens so that visibility decreases to a kilometer or less, it's called fog. Fog is nothing more than a cloud at ground level, but there are considered to be several types of fog because of the different ways it can be formed. The first type is called advection fog. That's the kind that rolls in over the golden gate. That fog forms because of the water at the surface of the sea is warmer 50 to 100 miles offshore than it is near the coast. Air over those warmer waters will itself be warm and moist. But when westerly winds blow or advect it over the cooler waters, the air cools to its saturation point. Excess water vapor condenses out into fog.

That process also works farther eastward. In the winter, the waters of the Gulf of Mexico are warmer than the landmass to their north. As the warm, moist Gulf air blows over that land, the air may cool to its saturation point and produce fog. The other main fog type is called radiation fog. It often forms on clear nights when there's little breeze and when the ground can cool quickly. Moist air near the surface cools to the saturation point and fog is formed. It often develops in low-lying areas like valleys, and that's why it's called valley fog. It forms because cold air tends to sink and so the coldest air will be found in the bottom of low-lying regions. River valleys are especially susceptible to radiation or valley fog since they're not only low but also abundantly supplied with moisture. For weather-wise, I'm Drew Barlow.