In Barcelona, the weather is generally mild with hot summers and mild winters. Summers (June to August) are hot and dry, with temperatures often exceeding 30°C (86°F), so light clothing like shorts, t-shirts, and sandals or sneakers are suitable. 

Spring (March to May) and Fall (September to November) are pleasantly warm, so bring layers like light sweaters or jackets for cooler mornings and evenings. 

Winter (December to February) is mild but can be chilly, especially in the mornings and evenings, so pack a coat or heavier layers. Overall, comfortable and breathable clothing is key, along with sunscreen and sunglasses for sun protection.