To expand on the rain shadow effect - air going up over a mountain range cools and water condenses out of the air, falling as precipitation. Then as it comes down over the opposite side, it warms back up and is at much lower humidity (since it lost water as precipitation, and since warm air can hold more water). So you're going to get much less condensing water/clouds/precipitation on the back side of the mountain range. If you have a prevailing wind such that this is mostly happening in the same direction, you'll have a rain shadow desert.
You can even get rain shadow deserts over the ocean, on the lee side of a mountainous island.
tomsing98 t1_j1t1uqj wrote
Reply to comment by Racklefrack in Why are there deserts near the coast? How come they don't get more rain, despite being near to a large body of water with plenty of sun and evaporation? by milton117
To expand on the rain shadow effect - air going up over a mountain range cools and water condenses out of the air, falling as precipitation. Then as it comes down over the opposite side, it warms back up and is at much lower humidity (since it lost water as precipitation, and since warm air can hold more water). So you're going to get much less condensing water/clouds/precipitation on the back side of the mountain range. If you have a prevailing wind such that this is mostly happening in the same direction, you'll have a rain shadow desert.
You can even get rain shadow deserts over the ocean, on the lee side of a mountainous island.