In the north the climate is cool and rainy, though summers may be warm. Seasonal temperatures depend on the elevation.

The climate in the south is warmer and more moderate because of the influence of the Mediterranean sea.

Long dry seasons can happen in some southern areas

"Portugal: Land and Climate." CultureGrams Online Edition. ProQuest, 2016. Web. 11 May 2016. 

Visit in December to March with rainy days and cold temperatures, there are fewer tourists at this time so that means that most everything is cheaper.

May, June and September to see mild days and perfect temperature for outdoor activities, such as hiking. Festivals are also a big thing around the time of June.

June to August is the best time weather-wise to visit.

What to pack:

Comfortable shoes, beach shoes, layers, and pack light because of the cobble stones in Lisbon and there are probably not lifts in the hotel that you are staying at. So you should pack your stuff in bags that are easily to carry around with you. You will also need to pack sunscreen and sunglasses because of the sunny weather/climate. You should consider a medicine bag and some tap water. - usually water is good to drink but if you want to be really safe you should buy bottled water.- "What To Pack For A Trip To Portugal".Little Grey Box. N. p., 2015. Web. 11 May 2016.