Although Peru's seaboard is situated well within the tropical zone, it does not display an equatorial climate; average temperatures range from 21° C (70° F ) in January to 10° C (50° F ) in June at Lima, on the coast. At Cuzco, in the sierra, the range is only from 12° C (54° F ) to 9° C (48° F ), while at Iquitos, in the Amazon region, the temperature averages about 32° C (90° F ) all year round. The cold south–north Humboldt (or Peruvian) Current cools the ocean breezes, producing a sea mist with the inshore winds on the coastal plain. Only during the winter, from May to October, does this sea mist (garúa) condense into about 5 cm (2 in) of rain.
Latitude has less effect upon the climate of the sierra than altitude. The rainy season in the Andes extends from October to April, the reverse of the coastal climate. Temperatures vary more from day to night than seasonally. The snow line ranges from 4,700 to 5,800 m (15,500 to 19,000 ft). In the eastern rainforest, precipitation is heavy, from 190 to 320 cm (75 to 125 in) annually; rain falls almost continuously between October and April.
A warm Pacific west-to-east current called El Niño appears near the Peruvian coast every four to ten years around Christmastime (the name is a reference to the Christ child), occasionally causing serious weather disturbances.