For optimal weather and marginally fewer tourists, the best times to visit Barcelona, Catalonia, and Bilbao are April through June and mid-September through mid-December. Catalans and Basques vacation in August, causing epic traffic jams at both ends of the month. Major cities are relaxed and, except for tourists, empty in August, though Gràcia’s Festa Major in Barcelona and Semana Grande in Bilbao keep these two cities alive during the summer season. Some shops and restaurants shut down for part of the month, but museums remain open, and a range of star-studded music and theater festivals ensure that there's no slack in the city’s cultural calendar.
Summers in Barcelona are occasionally very hot, but temperatures rarely surpass 100°F (38°C), and air-conditioning is becoming more widespread. In any case, dining alfresco on a warm summer night is one of northern Spain’s finest pleasures. All in all, spring and fall offer the best temperatures at both ends of the Pyrenees. Barcelona winters are chilly enough for overcoats, but never freezing: ideal for walking, fireside dining, and hearty winter cuisine.