This should be a toggle (you should be able to enable it with any fog type available). Enabling this lets the fog dynamically densen or lessen depending at the time of day. So for example at 0 there is lots of fog while there is almost no fog at 6000. This should also be configurable.

I would like to add on to this, having more fog during rain and snow, but less fog during clear weather. Also having the color of the fog change to black as you go deeper underground.