Due to the its orography and enourmous variety of landscapes, Spanish climate varies much from one part to another. Generally one can say that the weather is good (specially if you are used to northern latitudes). The north of Spain is humid with mild temperqatures in summer and cold in winter.
In the central part of Spain, climate is more extreme, very hot in summer and quite cold in winter (though dry). However, it rarely falls below -7°C in cities but it does get over 40°C on the worst summer days of the year in the hottest parts.
The mediterranean coast has humid and hot summers with high temperatures. Winters are mild and enjoyable. Autumn in this coast is the time known for the 'Gota Fría' (the cold drop) for its torrential rains that get to flood some parts.
The south has dry hot summers and moderate dry winters and the Canary Islands have good weather throughout the entire year.
What to wear
In the north it is convenient to have a rain-coat and umbrella the year round. Though the last years have provided warmer summers, it still remains chilly in the nights. In northern regions winter might not be extremely cold at the seaside but in the inside it might snow or freeze during the night.
The rest of the coasts are milder. In summer you should have a hat or something to cover your head and a traditional fan ('abanico' in Spanish) comes very handy. In winter rain-coats and some warm clothing, even a coat.
Generally cultural events like theatre, cinema or restaurants don't deserve the honour of people dressing themselves up specially. However in some casinos you will not be allowed to enter with casual wear and men will need to wear a shirt and a tie. Some places like opera houses or classy restaurants will not allow people with sport shoes, but this is increasingly rare.
When to come
The best months to visit are April, May, June, September, October and November. Usually winter months in the coast and summer months in cities like Madrid are low season.
Easter holidays are usually packed, specially in Sevilla. So if you plan to go there then, we suggest you start looking for accommodation the previous Christmas.