How did the Atacama receive rainfall after 400 years?

The desert called The Atacama Desert is called Desierto de Atacama in the Spanish language. This is a location that is a desert plateau located in South America. This area covers a 1,000 kms (600 miles) locality. This location is west of the Andes mountains. This Atacama desert is surely one of the driest places in the entire world.

Now, the driest is the McMurdo Dry Valleys. Rainfall is quite unusual because of this locality an rarely can be counted as such a place. Only after 400 years did this place receive any rainfall. Thus it is surely one of the driest or the most dirtiest place on the earth.