The Northern Region has an Atlantic Climate. This means that you can enjoy mild winters and warm summers in the western part of the region, nearer to the shore. Meanwhile, if you travel to the inland of the North, winters get colder and longer, while summers get hotter.
Spring is somewhat rainy in March and April, though towards May the weather gets sunnier, and perfect for city tours. However, if you are looking for a beach town to enjoy the ocean and swim in, this might not be the right time for it.
Summer is the best season to travel here, mostly because you can visit everything: the national parks, the rivers, the wilderness as well as cities, maybe swim in the ocean if the rather cool water temperature doesn’t put you off.
If you don’t like high tourist seasons, then autumn is your pick. The weather is great, cities are comparatively free from traveling folks, and hotel prices get cheaper too. You can also check out some cities that celebrate St. Martin’s Day (Dia de São Martinho) on November 11th, accompanied by some great food, wine, and, most importantly, chestnuts!
Since it gets colder during the winter, traveling to Northern Portugal is not very common. However, there are some destinations worth visiting during this season. For example, Serra da Estrela: the highest mountain range in the mainland of Portugal, is so much prettier during the wintertime.