It is a rare treat to be able to go to the beach in the morning and skiing in the afternoon, but that is indeed what you can do in Granada. Despite being so far south, weather in Granada in the winter can get quite cold (as low as -15ºC or 5ºF) as the nearby Sierra Nevada mountains bring low temperatures into the city, at least at night - day times can still be quite pleasant. Skiing is possible until early May, with the temperatures in the city of Granada at this time pleasantly warm. You can usually expect constant sunshine throughout the summer, although as the picture above shows, you might occasionally need an umbrella even in August.
Seville is the only place I know of in Spain where people have said it was actually too hot to enjoy the city properly. As with Madrid, the locals are all smart enough to get out during the intense heat of July and August, leaving the city to hordes of tourists and little else. If temperatures in excess of 40ºC (100ºF) are normal to you (that'll be people from Phoenix then!) then come to Seville in August - if not, keep away.