Climate of Lisbon

Lisbon and its metropolitan area feature a mild Mediterranean climate (Köppen: Csb/Csa), with short, mild and rainy winters and warm to hot, dry summers. According to the Troll-Paffen climate classification, Lisbon has a warm-temperate subtropical climate (Warmgemäßigt-subtropisches Zonenklima). According to the Siegmund/Frankenberg climate classification, Lisbon has a subtropical climate.

Normals
Lisbon has mild to warm, moderated temperatures. Winters are mild especially for its latitude with average daytime temperatures between 15 and 16 C and nighttime lows between 8 and 10 C. Summers are warm to hot, but due to the upwelling phenomena in the western coasts of its metropolitan area, maxima in summer fluctuates considerably depending on the location. Regions across the Tagus Estuary, for example, typically average around 30 C maxima in July and August, while areas west of the city and close to the coast, such as Cascais or Sintra, will usually average around 23 - 25 C maxima, reaching as low as 21 C in Cabo da Roca. Costa da Caparica is an exception to this rule as it is far less exposed to the cooler ocean currents and is therefore warmer in the summer. Nighttime lows during summer are often independent on the location, generally around 16 - 19 C, but the typical urban heat island phenomenon felt by the capital can increase these lows significantly compared to rural areas of its district.

Extremes
Lisbon's location on the westernmost side of continental Europe makes it much less vulnerable to both heatwaves and coldwaves, though outbrakes of the Saharan Air Layer can sometimes push the temperatures above 40 C as it happened as part of the 2018 European heat wave, skies were a shade of white due to the extreme concentrations of airborne dust particles. Temperatures in two of Lisbon's stations reached an all-time high of 44.0 °C on 4 August of that same year. The third station (Tapada da Ajuda) recorded 43.3 °C. The coldest temperature ever recorded in the city was -1.5 °C on both 15 February 1860 and 15 January 1985

In a normal year, the recorded maxima can go anywhere from 12 - 19 C in the winter and 23 - 35 C in the summer, and the minima from 3 - 13 C in the winter and 16 - 24 C in the summer. Temperatures beyond these are usually considered irregular and limited to exceptional years. Lisbon is on the USDA hardiness zone 10b.

Precipitation
Lisbon can be described both as a moist and a dry city depending on the season of the year. Precipitation is most common in Autumn and Winter. Summers in Lisbon tend to be very dry due to the Azores High though exceptions happen and low-pressure areas can come into play bringing much more rainfall than normal but still avoiding a wet summer (>30 mm). Foggy mornings are also common in the summer, especially in coastal areas and can bring drizzle which can sometimes be observed early in the day in wet roads and calçadas.

Lisbon has on average 112 precipitation days a year of which around 30% is drizzle (below 1 mm). The driest months, July and August, have on average two days of precipitation (4 - 6 mm of which 50% is drizzle), and the wettest months, November and December, have on average 12–15 days of precipitation and around 127 mm. December is the rainiest month of which half the days receive some form of precipitation. The average annual rainfall is 774 mm.

Humidity
In the same way precipitation varies greatly from month to month, the average relative humidity also experiences considerable seasonal changes. Lisbon has very humid winters, averaging 78-80% humidity. The air in the summer is otherwise dry, 60 to 65%, and is particularly variable, often going below 40% during the day and surpassing 70% at night.

Sunshine
Lisbon is a sunny city, in fact, it is the sunniest capital city in mainland Europe and one of the sunniest overall places in southern Europe, with more than 2,800 yearly sunshine hours despite the relatively high yearly precipitation. Sunshine and precipitation stack up oppositely with the dullest month being also the rainiest (December) which has around 140-150 total hours. Despite July having the most sun hours, August is on average the sunniest month with around 80% chance of direct sunlight hitting the ground.

In the Lisbon area, sunshine hours reach their maximum value in the southwestern Setúbal Peninsula (near Cabo Espichel), and their lowest in the Sintra Mountains and parts of the northwest District.

Daylight
Due to its southern position in Europe, Lisbon has a rather optimal number of hours of daylight. Winter days are not as short as in the northern part of the continent and summers have at least 9 hours of nighttime. The average duration of daylight in the wintertime is 10.3 hours (for comparison: London or Moscow or Warsaw have about 8 hours).

Wind
Lisbon is generally still, though it can become quite windy in occasional Atlantic storms, accompanied by rain. The average wind speed depends largely on the area. Tapada da Ajuda has almost no sign of wind, other areas such as Gago Coutinho, near the airport, get double that wind speed. The District of Lisbon, especially the west, is one of Portugal's windiest zones. Cabo da Roca has registered wind gusts of up to 169 km/h.

Sea temperature
As with the rest of Portugal, ocean temperatures are extremely moderate and cool year-round, only varying 5 C-change between the coldest and warmest month. The coolest months are February and March (around 15 - 15.5 C) while the warmest are from August through October (around 19 - 20 C). The average annual sea surface temperature is around 17.5 °C.

Lisbon Metropolitan Area
Temperature and precipitation variation across various sections of the metropolitan area of Lisbon: