How do mountain deserts like the Atacama stay so dry?

The Atacama Desert in northern Chile is extraordinarily dry because several factors work together. Moisture from the Atlantic is largely blocked by the Andes, while cold ocean waters and atmospheric circulation patterns limit rainfall from the Pacific side. In some locations, average rainfall is extremely low, and some weather stations have recorded years or even decades with little to no measurable rain. High elevation, strong sunlight, and thin air add to the harsh conditions. This combination makes the Atacama one of the most famous high-altitude deserts in the world.