In Lisbon rainiest months of the year are December and November during which monthly rainfall average reaches 128 mm. On the other side, driest months are August and July when the average rainfall is reduced to 4 mm per month.

The rainiest month in Lisbon, Portugal, is typically November, followed closely by December and January. During November, the city experiences an average rainfall of approximately 127.6mm, distributed over roughly 13 to 15 rainy days. This period marks the transition into the Atlantic winter, where moist air masses from the ocean frequently bring persistent showers and occasional heavy downpours. While Lisbon is known for its high number of sunny days, the late autumn and winter months see a significant increase in humidity and cloud cover. If you are visiting during this time, it is highly recommended to carry a sturdy umbrella and waterproof footwear, as the city's famous limestone "calçada" pavements can become quite slippery when wet. Conversely, the summer months of July and August are incredibly dry, often seeing less than 5mm of rain, making the seasonal contrast in Lisbon's Mediterranean climate quite stark.