system
Given the following post, respond as if you're commenting on Reddit:
human
What causes the thick mist/fog that I frequently see coming off of mountains in my area?

I live in the temperate rainforest biome that's in the Pacific Northwest of North America. I frequently see intensely heavy mist/fog[?] drifting up off the mountains close to me. What causes that? Is it a mist or a fog or low clouds, or what? Does this happen to other mountains or only those in similar rainforest areas?
gpt
The amount of water that a given volume of air can hold depends, among other things, on its temperature. Warm air can hold more water than cold air - this is why speak of relative humidity, with 100% being the max amount of water the air can hold at the current temperature.

When you get wind blowing towards mountains, the mountains will cause the air to rise, just like driving over a ramp. As the air rises, it cools. As it cools, the amount of water it can hold lessens. If the air was fairly humid to begin with - something that often occurs in the pacific north west- it won't take much rising until there's more water in the air than it can hold. The excess water condenses into tiny droplets that make up fog or clouds (same thing, basically).