Here's how it works:

* Windward side: As moist air rises up the windward side of a mountain, it cools. As it cools, the air can hold less moisture, leading to condensation and rainfall.

* Leeward side: The air that has lost much of its moisture descends on the leeward side of the mountain. This descent warms the air, further reducing its capacity to hold moisture. The result is a drier environment with significantly less rainfall.

So, the less rainfall on one side of a mountain is referred to as the rain shadow effect.