The region´s geographical location dictates climatic characteristics of transition, between the cold and moist climates of Northern Europe, and those hot and dry from Africa.
Although, under the climatic point of view, the Mediterranean influence is felt throughout the country, in the peninsular Northwest, it is evident the Atlantic influence.
Variations in average annual temperatures are small, due to the regulatory effect of the Atlantic, standing between 7,5ºC and 15ºC. The thermal amplitude increases as one goes from the coast to the interior and advances in altitude.
In general, it can be said that the winters are mild and summers are cool. The mountain barrier that delimits the region, affects the region´s climate, causing condensation of the masses of moist air from the ocean, and high rainfall.
The rainfall distribution is uneven throughout the year, being extremely concentrated between December and March (ca. 50% of the annual precipitation). In contrast, the summer months, from June to September, register less than 12% of annual precipitation. Frost is absent on the coastline, however its presence increases as one moves inland and in higher altitudes. In some areas, the frost period may last three months, usually from October / November to March.
Solar insolation, reaching minimum values in winter and maximum in July, registers an average value of 2400 sunshine hours per year, decreasing from the coast to the interior.