Lima
Climate

Lima has a mild climate, despite its location in the tropics and in a desert. Lima's proximity to the waters of the Pacific Ocean leads to intense maritime moderation of the temperatures, thereby making the climate much milder than those to be expected for a tropical desert, and thus Lima can be classified as a desert climate (Köppen: BWh) with subtropical temperature ranges. Temperatures rarely fall below 12 °C (54 °F) or rise above 30 °C (86 °F). Two distinct seasons can be identified: summer, December through April, and winter from June through September/October. May and October/November are generally transition months, with a more dramatic warm-to-cool weather transition in later May or/and earlier June. Situated onshore from the cold ocean waters, rainfall is extremely rare in Lima.

The summers, December through April, are sunny, hot, and muggy. Daily temperatures oscillate between lows of 18 to 22 °C (64 to 72 °F) and highs of 25 to 30 °C (77 to 86 °F). Coastal fogs occur in some mornings and high clouds in some afternoons and evenings. Summer sunsets are colorful, known by locals as "cielo de brujas" (Spanish for "sky of witches"), since the sky commonly turns shades of orange, pink, and red around 7 pm.

During winter, June through October, the weather is dramatically different. Grey skies, breezy conditions, higher humidity, and cooler temperatures prevail. Long 10 to 15-day stretches of dark overcast skies are not uncommon. Persistent morning drizzle (garúa) frequently occurs from June through September, coating the streets with a thin layer of water that generally dries up by early afternoon. Winter temperatures vary little between day and night. They range from lows of 14 to 16 °C (57 to 61 °F) and highs of 16 to 19 °C (61 to 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 in the early summer and a usually persistent low cloud deck during the winter (generally develops in late May and persists until mid-November or even early December). The predominantly 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 184 hours in April, which is exceptionally little for its latitude. By comparison, London has an average of 1653 hours, and Moscow 1731. Winter cloudiness prompts locals to seek sunshine in Andean valleys above 500 meters (1,600 ft) above sea level.

While relative humidity is high, rainfall is very low due to strong atmospheric stability. The severely low rainfall impacts the city's water supply, which originates from wells and from rivers that flow from the Andes. Inland districts receive anywhere between 10 and 60 mm (0.4 and 2.4 in) of rainfall per year, which accumulates mainly during the winter. Coastal districts receive only 10 to 30 mm (0.4 to 1.2 in). As previously mentioned, winter precipitation occurs as persistent morning drizzle. These are locally called 'garúa', 'llovizna' or ' camanchacas '. On the other hand, summer rain 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 turn, 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.

Lima's climate (like most of coastal Peru) gets severely disrupted in El Niño events. Coastal waters usually average around 17–19 °C (63–66 °F), but get much warmer (as in 1998 when the water reached 26 °C (79 °F)). Air temperatures rise accordingly.
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