Mountains near a large body of water can act as a huge shower curtain for an entire region. On the western, ocean side of the Cascade Range in America's Pacific Northwest, moisture-carrying winds blow in from the Pacific. As the air strikes the mountains, it rises and cools. Cloud droplets form, then raindrops. Rain falls steadlily on Seattle. The air continues over the mountains, but now it's been squeezed dry. Things are much browner on the other side. This mirror opposite is called a "rain shadow."
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