Cool air can hold less water vapor than warm air. Apply this fact to explain why clouds and precipitation form on the windward side of the mountain.​

The pressure is directly proportional to temperature (when the pressure decrease the temperature decrease too). Because the air parcel expands so the molecules will not interact with each other as much.

The energy of the particles does not change but the fact that the particles are more spaced out means the parcel is cooler.

so now, the warmer a parcel of air the more water vapor it can hold. so, if a parcel of air cools it's ability to hold water vapor drops and if it drops to a low enough point that is when the water vapor will condense and turn back into liquid water. This is how clouds and precipitation form on the the windward side of the mountain.