Rainshadow is the area on the side of the mountain away from the wind that receives little rainfall. When Mountains blocks passage of rain it produces cast also known as shadow and weather system of dryness behind them. Moist air and wind are being drawn to the top of the mountains by prevailing winds where it precipitates and condenses before crossing the top.
Without much moisture left the air advances across mountains which create drier side known as rainshadow. The condition exists because warm moist arises to the top of the mountain range by orographic lifting. The air is expanded and adiabatically cools when atmospheric pressure decreases with an increase in altitude and then the air reaches its adiabatic dew point.
On diabatic dew point, moisture precipitates on top and windward sides of the mountain. Due to the precipitation that air hs lost much of its moisture, it descends on the leeward side, when moisture it descends it gets warmer due to adiabatic compression.
