The city of Cusco has a fairly cool weather during most of the year. However, the climate varies in other areas of the region, such as Machu Picchu or the Sacred Valley.
The average annual temperature in the city is 12ºC (54ºF), while the average annual low temperature is 5ºC (42ºF), although in reality the minimum temperature can be below 0ºC ( 32ºF). The average maximum temperature is 18ºC (66ºF), but the maximum can reach 23ºC (73ºF).
The Cusco region has only two well-defined seasons: the wet season and the dry season. The rainy season begins in October, when spring begins in the southern hemisphere and ends in March.
At this time the rain falls almost every day for three or four hours, mainly between December and March, but there are also several sunny days.
The average rainfall during this time is 98 mm (3.85 in). The temperature fluctuates between 7ºC (45ºF) at night and 21ºC (70ºF) at noon. Also, since february it is forbidden to trek on the Inca Trail to Machu Picchu, which is the most famous trekking route in South America.
The dry season starts around March and lasts until September, during this time there is almost no rain and the sky is completely clear every day. However, between May and July it is very cold. In Cusco these months are called Frost Time. During these months the temperature drops quite a bit, especially at night, when it can drop to -5ºC (23ºF, at the freezing point). Paradoxically, at midday temperatures can reach up to 23º C (the annual maximum).
A peculiar phenomenon known as “Cabañuelas” occurs in the first week of August, since the weather is generally irregular for a few days. The “cusqueños” (citizen of Cusco) believe that the weather of one of these days represents the weather that a specific month will have next year. For example, if it rains on the first Monday of August, this means that it will rain a lot in January. The same thing happens with Tuesdays and February and the rest of the days and months.
The mean morning relative humidity is 79% and the mean afternoon relative humidity is 45%. The average wind speed is 18 Km/ph (11 mph), with the maximum wind speed being 20 Km/h (13 mph), occurring between August and October.
Other areas of Cusco have different climates, for example the area of Machu Picchu has a more humid climate, since it is located at a lower altitude and close to the Amazon jungle. There, the average temperatures are between 23º C (73º F) and 25º C (77º F), with the minimum temperature around 18º C (64º F). Also, it rains more often in this area.
The Sacred Valley also has two seasons: wet and dry, but it has a milder and more pleasant climate than Cusco, with average temperatures ranging between 14ºC (57ºF) and 22ºC (72ºF). .
The dry season is the best time to visit Cusco and all the areas that surround it, since during this season the weather is very mild. In addition, most events and celebrations such as Inti Raymi on June 24 (festival of the sun and the day of Cusco) take place between May and November.