Final answer:
Clouds form on the windward side of a mountain due to the rain shadow effect. Moist air from the ocean rises and cools, causing precipitation on the windward side. The leeward side of the mountain becomes dry, resulting in a rain shadow.
Step-by-step explanation:
Clouds form on the windward side of a mountain due to a phenomenon known as the rain shadow effect. When moist air from the ocean rises up over the mountain range, it cools and condenses, causing precipitation to fall on the windward side. As the air reaches the leeward side of the mountain, it becomes dry, resulting in little precipitation in that area. This creates a rain shadow, where the leeward side of the mountain remains arid.