Weather and climate
The climate in the Cordilleras Blanca and Huayhuash is determined by its proximity to the equator and also by the relationship between the humid air of the Amazon basin and a perpetual low-pressure zone over the Pacific coast, the latter caused by the cold Humbolt current, which draws moisture laden air westward over the mountains.
The rainy season spans from October through March, and the dry season (also known as the “Andean summer”) spans from April through September. During the Andean summer the weather is stable with only one or two mediocre days in a week and sometimes with weeks of perfect weather. It is during these summer months that the majority of the trekking and climbing takes place.
A typical Andean summer day begins with a cloudless blue sky and warms until midday often reaching 20ºC at 4000m/13,123ft. The mornings and late afternoons can be chilly at this altitude with temperatures dropping to 0ºC. Wind is not generally a concern at this time of the year.