Here’s another video for you:
The fog thickness and altitude are random. Once you switch them on in creative, fog and rain/snow will stay forever, or until switched off. Can be useful for adventure maps.
After some playtesting, I think in survival modes the fog is very dangerous. It’s extremely easy to get lost. Or suddenly meet face to face with a tiger.
The very thickest fog limits visibility to just a few blocks, and it can persist for nearly the entire day in autumn and winter, if one is unlucky. There is much less fog in the summer.