Summertime is the perfect time in Northern Spain, except for the big crowds in a few premiere cities and destinations. To avoid the crowds but still have mostly good weather, both spring and autumn are good options. As for winter, if you don't love rain and wind, I'd suggest you choose somewhere else to go.

The best time to visit Northern Spain (also known as "España Verde" or Green Spain) is generally from late May to late September. During this period, the regions of Galicia, Asturias, Cantabria, and the Basque Country experience their mildest and driest weather, offering a refreshing escape from the sweltering heat found in Andalusia or Madrid. In the peak of summer (July and August), temperatures in the north typically range from 22°C to 26°C, which is ideal for hiking the Picos de Europa or visiting the Guggenheim Museum in Bilbao. For those looking to avoid the biggest crowds and save on accommodation, the "shoulder seasons" of June and September are particularly rewarding, as the landscapes are at their lushest and the local sidra (cider) and pintxos scenes are vibrant. If you are planning to walk the Camino de Santiago, May and September are widely considered the "sweet spots" to avoid both the summer heat and the winter rains. However, you should always be prepared for a bit of rain regardless of the month, as the region's Atlantic climate is what keeps its rolling hills so remarkably green and beautiful throughout the year.