For optimal weather, fewer tourists, and a sense of local life as it is, the best times to visit Barcelona are April-June and mid-September-mid-December. Catalans themselves 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 keeps the neighborhood very much alive during the festivities. Small shops and some restaurants shut down for the entire month, musical venues are silent, but museums remain open.
Summers in Barcelona, though occasionally very hot, are usually not too steamy for comfort. 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 weather and temperatures. Barcelona winters are chilly enough for overcoats, but never freezing: ideal for walking, fireside dining, and hearty winter cuisine.