We've all seen fog come and go, but what is it? How does it occur? Fog is nothing more than a collection of water droplets and/or ice crystals. It's basically the same thing as a misty day, except the visibility is much worse in fog than it is when it is misting. This makes it the same as a cloud, but on the ground. That begs the next question. How does a cloud form on the ground?
Fog forms when water vapor near the ground cools and condenses (changes phase) from a gas to a liquid, hence the tiny water droplets. How this happens can differ depending on the type of fog. A great source for this is:
In most cases, the fog will "burn" off as the sun rises. The temperature of the water droplets increase and change phase back into a gas.