There are two main seasons in Peru: the rainy season and the the dry season. The rainy season runs between October and April, with the dry season usually running between May and September. Temperatures during the dry season run from around 12 C (50 F) at night to the mid 30s C (upper 80s F) during the day. Given its exposed location, it can get quite hot in Machu Picchu, and at its elevation, the sun is strong -- do not forget your sunscreen!
The dry season is the best time to travel to Machu Picchu -- and not surprisingly, coincides with the high season. To avoid the crowds, consider traveling in late April, May, June, or early October. Crowds are the heaviest during July and August.
The weather forecast on this chart is lower by 10 F on the low and the highs. According to the Peruvian Senamhi, which is the National Institute providing the right information, the weather chart mentioned on this chart is for Cusco City, not Machu Picchu which is 4100 feet lower in altitude and as such, much warmer temperatres.
