Cusco, where it's located

In Cusco (or Cuzco), the ancient capital of the Inca Empire, located at 3,300 meters (10,800 ft) above sea level in the Andes, the climate is temperate, spring-like during the day all year round, but with cold nights in winter, from May to August, when the minimum temperatures are near freezing (0 °C or 32 °F); on the contrary, in summer, from November to March, which is also the rainiest period, night temperatures are milder, around 7/8 °C (45/46 °F).
As mentioned, during the day, the temperatures are uniform throughout the year, and reach 20/22 °C (68/72 °F) when the sky is clear. This happens even in winter because of the big increase in temperature caused by the mountain sun. In contrast, in winter, a cold mountain breeze starts to blow at sunset, and on winter nights, there may be slight frosts.
During the day, the temperature never reaches 30 °C (86 °F), even though the mountain sun at tropical latitudes is very strong and requires appropriate protection.
Here are the average temperatures.
Cusco - Average temperatures
Min (°C)776531125667
Max (°C)191919191919192020212120
Min (°F)454543413734343641434345
Max (°F)666666666666666868707068

Rainfall is moderate, since it amounts to 710 millimeters (28 inches) per year; it is concentrated in the summer months, in particular, it is equal to or higher than 100 mm (4 in) per month from December to March. In these months, showers occur almost daily, although they are often short-lived. In the winter season, from May to August, it rains very rarely. The rains begin to fall in September, although they are initially rare and brief.
Here is the average precipitation.
Cusco - Average precipitation


The amount of sunshine in Cuzco is good in the dry season, from May to August, when blue skies prevail, it is decent in the intermediate periods, when the rains are frequent but short-lived, while from December to March, there is not much sun because of the frequent cloudiness, which can lead to rain showers. Here are the average sunshine hours per day.
Cusco - Sunshine

Best Time

The best time to visit Cuzco is from May to October, since it is the driest and sunniest time of the year. However, it is winter, so you should be equipped for the cold at night, and be ready to uncover (but at the same time to protect yourself from the sun) during the day, when the air becomes mild.
In April and September, there are some showers, but generally of short duration and not heavy.