Although this is a mainly dry area, we can have torrential rain even in the summer. From time to time the Pyrenees also has a very strong, dry wind , the Tramontane, similar to the Mistral. Be prepared by bringing some suitable clothes.
We are, however, much further south than Great Britain, and the sun is higher, so sensitive skins can burn, even in winter!
As for eating out, etc, this area is very relaxed, and there is no need to dress up, even for very good restaurants.
Jeans or shorts are acceptable anywhere, anytime.
Useful weather forecast sites are:-
France Meteo .