There is really no bad time to visit Spain. It just depends on what you want to see and where you want to go and your tolerance for certain things.
Spain can be really hot in the summer but, unlike the idea that most people have, the whole country is not hot and sunny all the time. Quite the opposite actually, especially in certain regions. The north coast — Galicia, Asturias, Cantabria, and the Pais Vasco — is beautiful and home to some of my absolute favorite cities and beaches in the world, and can be chilly and rainy during the summer. If you want guaranteed sun and will be upset with clouds or rain, than summer in the north may not be for you.
The South of Spain can get extremely hot in the summer. It frequently gets above 40 degrees Celsius, or over 100 F, in cities across Andalucia, the southern region of Spain, during the summer. Although it’s dry heat, it can be stifling. Many homes, businesses, and restaurants don’t have air conditioning. Because of this, I would not recommend visiting the non-coastal cities in the South of Spain during the summer, unless it’s part of a longer beach-focused vacation that includes a few days touring nearby cities.
The Mediterranean cost of Spain is stunning, particularly the northern part in Cataluna. With the Mediterranean can come humidity, especially around Valencia and Alicante.
Spain can be cold in the winter, something that may come as a shock to some. In the regions north of Madrid, it can get quite cold. Mountain ranges are frequently filled with snow-covered peaks. Even the Sierra Nevada, visible from the southern city of Granada, has snow-capped peaks well into spring. Although if you’re traveling you probably won’t be staying in a home (unless you’re in an Airbnb), but many homes in the South of Spain don’t have central heat. Families rely on space heaters and braseros, or a table with a heater underneath and a big blanket skirt, to keep warm.
You may want to avoid Sevilla during the Feria de Abril, unless you are traveling to Sevilla with the intention to attend the Feria. If you don’t want to attend this week long festival event, then this is not a great time to visit the city as it will be packed, many restaurants and bars will have shortened hours, or will be closed all together. If the Feria is an experience you want to live, then, by all means, go during that week!
Holy week, or the week before Easter is another time to consider carefully. Many cities have processions in the days leading up to Easter. They can be fascinating to watch and an interesting window into the culture in certain ways, but especially smaller cities tend to shut down in the days leading up to Easter.
All of this is to say that, like any country, there are always weather-related or timing issues to consider when planning a trip. If you absolutely want sunny beach days, certain times of year and certain parts of the Spanish coast are best. If you want to spend substantial time in southern cities but don’t like intense heat, spring and fall are probably the best bets for you. If you want to either avoid or attend popular tourist events, that’s something else to consider.
There is no perfect time to travel. All times and seasons of years have their pluses and their minuses. The goals of your trip can be accomplished with good planning.
And, like most things that relate to travel, it’s always best to come prepared with layers, comfy shoes, and a positive and flexible attitude.