Lisbon is favored with mild weather all year, and each of the four seasons brings its own beauty. Set in the valley of the Tagus River and close to the Atlantic Ocean, the city enjoys a Continental climate and although summers can get uncomfortably hot, the temperature rarely drops below freezing in winter. It never snows except for a couple of flurries, a phenomenon that happens only every few decades. Still, winter is damp and chilly—be prepared for wet weather November-April.
The best months to visit Lisbon are May and June (June is the best because it's full of celebrations). Spring is usually moderate, although April is known for its rainy periods. In summer, the afternoon heat can be unpleasant at times. Autumn is fine, though it can be rainy then, too.