Why is leeward side of the mountain usually dersert-like or semi-arid?

The leeward side of a mountain is in a rain shadow, where moist air is forced to rise over the mountain and loses moisture as it cools and condenses. As the air descends on the leeward side, it warms and dries out, creating dry conditions. This results in less rainfall and a drier climate, leading to desert-like or semi-arid conditions.