Pack for the day you will actually spend, not just the temperature on the forecast. A sunny afternoon by the river, a windy evening by the sea and a steep walk on wet paving ask for different clothes. Lisbon's 1991–2020 climate normal from IPMA describes typical seasons, not the weather on your travel dates.
What should I pack for each season?
Spring (March–May): choose layers you can remove during a warm afternoon and put back on after sunset. A light waterproof layer is useful if showers are forecast. Summer (June–August): bring breathable clothes, sun protection and water for long outdoor days; keep a light layer for a breezy coast or air-conditioned interiors. Autumn (September–November): early autumn can still feel summery, while later visits call for a rain layer and warmer evenings. Winter (December–February): bring a proper jacket, a rain layer and clothes that can be combined; Lisbon is not reliably dry simply because the day begins bright.
You do not need a special wardrobe for the city, but comfortable shoes with good grip make a difference on steep streets, steps and calçada, especially in rain. If you are visiting Sintra's hills or the Cascais coast, pack for those conditions too; they may feel different from central Lisbon on the same day.
What should I check before leaving the apartment?
Use the IPMA forecast for Lisbon for the temperature range, rain probability and wind, then check IPMA weather warnings for the district and your destination. A climate average cannot tell you whether this afternoon will be wet or unusually hot. Check again the evening before a long outdoor outing.
If rain is likely, keep an indoor stop in your plan and allow longer on slippery hills; our walking and accessibility guide helps with the route. For a very hot day, move strenuous uphill walks away from the hottest hours and take water breaks. On a windy or rainy beach day, a seafront walk may still be pleasant, but do not treat a sunny city-centre forecast as proof of good swimming conditions.