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Why is there so much fog and rain in Sintra?

16 Jan 2023

Lui̚s Duarte PSML 6340 (1)

Rain and fog are two of the hallmarks of Sintra. Truth be told - they’re part of its charm. Nobody is surprised to see that, regardless of the season, the morning in Sintra starts with drizzle. Those who live here already know the saying used during the summer season: “[the weather] will clear up after lunch”.


But why does it rain so much in Sintra? Why does the fog 'helmet' form over the mountains and beaches?


First, you have to keep a very important point in mind: the municipality of Sintra is huge. It covers over 300 km2 with more than 380 thousand inhabitants. It is subdivided into 11 parishes and borders the municipality of Mafra to the north, Loures, Odivelas and Amadora to the east, Oeiras to the southeast and Cascais to the south. To the west, it’s bathed by the Atlantic Ocean. Therefore, the rainy scenario is not experienced by everyone in the same way.


But the truth is that Sintra has a special climate, a fog that distinguishes itself from all others. And why is this? The proximity to the Atlantic Ocean is one of the factors that contributes to the existence of this microclimate, but the most important point in this analysis is the role of the Sintra Mountains as an orographic barrier. When air masses coming from the sea and from the north 'meet' the mountains, they’re forced to rise, which causes condensation. And why does the weather 'clear up’ in the afternoon? Thanks to the increase in temperature - air masses become less cold and when they reach the mountain there is no longer such an acute thermal shock.  


The high levels of rainfall and humidity allow for the existence of unique vegetation, made up of thousands of species - more than 340 species of trees have been identified in Pena Park alone! And here, a 'snake eating its own tail' feedback loop is generated: the 'green spot' also helps to regulate temperature, control the volume of water in the soil and maintain humidity levels in the mountains. Thus, the perfect conditions are met for the creation of a setting worthy of a fairytale.


Here's a tip: if you like the rain and walking around in cooler weather, visiting Pena Park on a foggy day is delightful. And as you know: if you come to visit Sintra first thing in the morning and get a lot of humidity or a little rain, don't worry - “it’ll clear up after lunch”.