The westernmost capital of mainland Europe occupies a stunning position on the Atlantic coast where the Tagus river empties into the Atlantic Ocean.
Lisbon is one of Europe's warmest capitals--and offers the tourist a great value. Lisbon's weather is moderated by its location on the Atlantic, and you won't see any extremes in the graphs below. Although mild, winter months do tend to be rainy.
Spring and early Fall are the best times to visit. June is optimal, as the festival season is heating up in Lisbon. August can be hot (but dry). Late September through October is also a good bet. If you must go in Summer, reserve your lodging in advance, as this is the major vacation time in Europe. You'll find links to user-rated lodging below.
The charts below show the historic high and low temperatures in Lisbon and the historic rainfall totals.
LocalTraveling Santo Estevao (value)
Hostel Inn Bairro Alto (value)