The diagram illustrates how a rain-shadow desert is formed.
Overall, the process begins when moist air from the sea moves towards a mountain and ends with the formation of a dry desert on the other side of the mountain. Rain falls only on the windward side, while the leeward side remains dry because the air has lost most of its moisture.
At the first stage, winds carrying moist air approach the coast from the sea. As they reach the mountains, they are forced to rise up the windward side. While rising, the air cools, causing clouds to form. As the temperature continues to fall, the moisture in the clouds turns into rain, which falls on the windward slope.
After that, the air crosses the top of the mountain and moves down the leeward side. Since most of its moisture has already fallen as rain, the air becomes dry. It continues travelling across inland areas without producing any further rainfall. As a result, the land receives very little precipitation over a long distance, eventually leading to the formation of a rain-shadow desert.