Final answer:
Leeward sides of mountains are cooler and drier due to the rain shadow effect, where moist winds lose their moisture on the windward side, leading to arid conditions on the leeward side.
Step-by-step explanation:
Leeward sides of mountain ranges are cooler and drier than windward sides. This phenomenon is due to the rain shadow effect, where the moisture-laden winds ascend the windward side of the mountains, the air cools and water vapor condenses to form precipitation. By contrast, after the air passes the mountaintop and descends the leeward side, it heats up and retains little moisture, leading to arid conditions.
The rain shadow effect explains why areas like the eastern coasts of islands with significant mountain ranges, such as the Western Highlands of the Congo or the Hawaiian island of Kauai, experience substantially drier climates compared to their western counterparts. Similarly, in North America, the mountains act as a barrier to moisture, creating semi-arid conditions in regions like eastern Washington and eastern Oregon.