Lima's climate is mild and comfortable, despite being located in the tropics and in a desert. Although classified as a subtropical, Lima's proximity to the cool waters of the Pacific Ocean leads to temperatures much cooler than those expected for a subtropical desert, and can be classified as a cool desert climate. It is neither cold nor very hot. Temperatures rarely fall below 12 °C (54 °F) or rise above 30 °C (86 °F) throughout the entire year. Two distinct seasons can be identified: summer, from December through April; and winter from June through October. May and November are generally transition months, with the warm-to-cool weather transition being more dramatic.

Summers are warm, humid and sunny. Daily temperatures oscillate between lows of 18 °C (64 °F) to 22 °C (72 °F), and highs of 24 °C (75 °F) to 29 °C (84 °F). Skies are generally cloud free, especially during daytime. Occasional coastal fogs during some mornings and high clouds during some afternoons and evenings can be present. Lima summer sunsets are well known for being colorful. As such, they have been labeled by the locals as "cielo de brujas" (spanish for "sky of witches"), since the sky commonly turns into shades of orange, pink and red around 7 pm. Winter weather is dramatically different. Gray skies, breezy conditions, high humidity and cool temperatures prevail. Long (1-week or more) stretches of dark overcast skies are not uncommon. Persistent morning drizzle occurs occasionally from June through September, coating the streets with a thin layer of water that generally dries out by the early afternoon. Winter temperatures in Lima do not vary much between day and night. They range from lows of 12 °C (54 °F) to 16 °C (61 °F) and highs of 16 °C (61 °F) to 19 °C (66 °F), rarely exceeding 20 °C (68 °F) except in the easternmost districts.

Relative humidity is always very high, particularly in the mornings. High humidity produces brief morning fog during the early summer and a usually persistent low cloud deck during winter (generally developing in May and persisting all the way into late November or even early December). Predominant onshore flow makes the Lima area one of the cloudiest among the entire Peruvian coast. Lima has only 1284 hours of sunshine a year, 28.6 hours in July and 179.1 hours in January, exceptionally low values for the latitude. Winter cloudiness prompts locals to seek for sunshine in Andean valleys located at elevations generally above 500 meters above sea level.

Although relative humidity levels are high, rainfall is very low due to strong atmospheric stability. The severely low rainfall impacts on water supply in the city, which originates from wells and from rivers that flow from the Andes. Inland districts receive anywhere between 1 to 6 cm (2.4 in) of rainfall per year, which accumulates mainly during the winter months. Coastal districts receive only 1 to 3 cm (1.2 in). As previously mentioned, winter precipitation occurs in the form of persistent morning drizzle events. These are locally called 'garúa', 'llovizna' or 'camanchacas'. Summer rain, on the other hand, is infrequent, and occurs in the form of isolated light and brief showers. These generally occur during afternoons and evenings when leftovers from Andean storms arrive from the east. The lack of heavy rainfall arises from high atmospheric stability caused, in term, by the combination of cool waters from semi-permanent coastal upwelling and the presence of the cold Humboldt Current; and warm air aloft associated with the South Pacific anticyclone.

The climate of Lima (as that of most of the Peruvian coast) gets severely disrupted during El Niño events. Water temperatures along the coast, which usually average around 17-19 °C (63-66 °F), get much warmer (as in 1998 when the water temperature reached 26 °C (79 °F)). Air temperatures rise accordingly. Such was the case when Lima hit its all-time record high of 34 °C (93 °F). Cooler climate develops during La Niña years. The all-time record low in the metropolitan area is 8 °C (46 °F), measured during the winter of 1988.