The climate varies from place to place in Peru, as the geography is incredibly varied. Also, the seasons are not entirely predictable, so one should be prepared for changes in climate.
In Cusco and its environs (including Machu Picchu, the Inca Trail, and the Sacred Valley), the dry season is roughly from mid-April to mid-November, and the rainy season runs roughly from mid-November to mid-April. The precipitation is not generally in the form of continuous rainfall; instead, there will be some rain and then it will generally be clearer for part of the day. The Andes become much greener during this time of year. Travel takes place to Peru all year round, with the only exception that trekking tours (such as the Inca Trail to Machu Picchu) generally do not take place during the wettest months of January to March.
Machu Picchu is at 8,000 feet, and Cusco is at 11,000 feet. At night in Cusco it can drop down into 40s and lower 30s during the dry season, so you should be prepared for cold weather. Temperatures are generally a bit warmer in the wet season. During the day temperatures will typically be in the 60s and 70s. On the Inca Trail, it can drop down into the 30s or 20s at night.
From October to May, Lima is sunny and hot. The wet season is from June to September, though in reality it doesn’t often rain. The precipitation comes in the form of a blanket of mist that is called the “garua.”
In the Amazon jungle, temperatures are generally high during the day (in the high 80s) and there is almost always very high humidity and at least some rain (this is a rainforest after all!). There is a wet season from November to April, when temperatures also get a bit higher, averaging in the 90s. In the dry season from May to October there will be somewhat less rain and it won’t be quite as hot. At night in the jungle during the dry season it can cool off quite a bit, dropping into the 60s at times.
If you have any questions about a specific place and time of year, please let us know and we’ll be happy to provide answers.