Would there be snow, rain, fog or clouds in a deep, sealed, subsurface cavern on the Moon if water were present?

Question

The question Most efficient method of storing energy with water on the moon? proposes a several hundred meeter tall subsurface cavern on the Moon. I added the following comment to an answer:

I keep thinking that there should be some way to use liquid/solid phase change as a way to store energy but I am bad at thermodynamics. Lunar subsurface temperatures are about 255 K near the surface and increase about 1.5 K per meter in depth (from here) so there are various temperatures above and below 273 K available in the walls of your 200 meter deep cavern if one did a little drilling. Who knows, it might be liquid at the bottom, and assuming the cavern is sealed and with evaporation there could even be rain!

Assuming the following:

1. the cavern was sealed so that an equilibrium vapor pressure were established
2. the floor was deep enough to expose the water to temperatures above the freezing point of water (273 K)
3. the ceiling was high enough to expose the water vapor to temperatures well below the freezing point of water

Question: Would there be continuous rainfall or snowfall inside? Would there be fog or clouds?

Answer 1

In Earth's atmosphere, fog and clouds form when saturated warm air flows into a mass of colder air. Condensation into droplets is also believed to be helped by the presence of fine dust particles.

In an enclosed cavern, the most likely place for condensation to form would be as dew and frost on the walls and ceiling, rather than as airborne droplets. Just slightly colder spots in the walls will collect the excess water vapor as condensation, as the warm air rises, before it can hit a cold front of air. If there are heat exchanger elements at the top (e.g. to collect the geothermal energy), they will be the most likely spot for ice to form, just as tends to happen inside a fridge.

Even in a truly massive cavern, the circulation of air will follow the geometry of the walls, so to create fog conditions (warm mass of air mixing with a cold mass of air) requires special design or luck. Of course, with special design it is also possible to shape the ceiling so that condensation "rains" down from it, instead of just running in rivulets down the walls. (Designs without occasionally dropping icicles may be harder to achieve.)

As I understand it, the force that makes warm air rise and cold air fall down in a pressurized container is based on gravity. This is also the basis of fractionation columns, which may not work as well on the Moon as they do on Earth (even if they are built six times taller). Because of the weaker gravity, the "lift" produced by geothermal heating is also weaker. On the other hand, separation of the fluids into cold and warm layers takes longer for the same reason. A lot depends on the shape of the hypothetical cavern, and the heat conducting properties of the walls. When water condenses, some ambient heat will be absorbed, which can serve to cool nearby air.