# Plant respiration

Rainforests are famous for making their own rain. Plants [transpire][1] something like 98% of the water they take up. When you have a lot of plants, and it is already pretty humid, the result is lots of mist.

[![enter image description here][2]][2]



# Cold ocean currents

Fog can form when the difference between the air temperature and dew point is less than 2.5 C. Water vapor in the air condenses into tiny droplets. This often happens when moist air passes over a cool surface; this is called advection fog. There are two common ways this happens: a warm front passes over an area covered in snow, or warmer ocean air passes over a coastal cold water upwelling. The fog of both California and the Pacific Northwest, as well as Maine and Newfoundland on the East coast both come from this warm air over cold current condition.  

# Enclosed Valley

Valleys ringed by mountains on all sides tend to not let stuff in the air escape. A famous example is smog in Mexico City.

[![enter image description here][3]][3]

However, this would work just as well for water vapor too. Have some region with misty air for any other reason, and then surround it with mountains. Lots of fog, all the time.

  [1]: https://en.wikipedia.org/wiki/Transpiration
  [2]: https://i.sstatic.net/Sm06u.jpg
  [3]: https://i.sstatic.net/DBMoU.jpg
  [4]: https://en.wikipedia.org/wiki/Fog
  [5]: https://en.wikipedia.org/wiki/Mist