The months April-June and September and October are the best times to visit. July and August are generally very hot, and it can be a bit cool in October in the higher elevations and Basque area. Sweaters will be needed for evenings. Winter, though generally mild, can be rainy, foggy and windy.
We think winter, even on the Costa del Sol, is on the cool side - much too cool to sunbathe and swim. It rains more on the Bay of Biscay coast than on the southern Mediterranean coast. The temperature cools dramatically at high altitudes.
The summers in Andalusia (southern Spain) are very hot while the winters are short. The rainfall except in autumn is low, (less than 700mm), not counting specific area such as Grazalema sierra, Aracena sierra, and the Sierra Nevada and La Sagra massif. The climate in these areas changes depending on the altitude and proximity to the coast, where temperatures are milder than inland. The average temperatures vary between 16ºC and 18ºC and decrease at altitude.