Turkey is spectacular every season but if you like to avoid hot temperature you may choose spring; April, May, June and autumn time; September, October, November during which you may have more tranquil holiday as the number of tourists decrease.
July and August are high season on Mediterranean and Aegean coast where you have the most beautiful beaches with clear turquoise water. During summer water degree it’s between 24-28°C. Some activities like boat cruises are only available until October.
If you wish to experience ”Hot Air Balloon Flight” in Cappadocia, know that it may be cancelled generally in winter due to strong wind currency, though summer is more likely to have the ride as wind gets smoother.
If you enjoy skiing, Turkey offers many ski stations like ”Erciyes, Uludag, Palandoken, Kartalkaya”. Best quality of snow you will find in January, February and March.
If you are planning to visit Black Sea region, note that it is heavily rainy in winter and autumn, so you may prefer summer time though it is still hot in the cities you will have fresh and cooler air in high plateaus where you have traditional festivals. Most popular places to visit in this region are Ayder Plateau, Lake Uzun, Lake Kara, Santa Ruins and rafting experience in Firtina River.
Southeastern part of Turkey is the hottest region in summer so it is better to visit in spring time. Famous cities from this region is ”Urfa, Gaziantep, Antakya, Mardin”.
Mediterranean coast is the warmest part of Turkey, always has mild temperature even in winter time but may be rainy. Most attractive places are Antalya and small towns around where there are a lot of holiday resorts.
Eastern part of Turkey has continental climate so if you wish to experience skiing, Erzurum Palandoken Ski Center will be a good option as it is heavily snowy in winter time. Summer is hot and dry and other popular places to visit are Ani Ruins, Van Lake, Kars,etc.
Aegean coast is also warm in winter time but quiet hot in summers so you can enjoy beautiful beaches where you have in Fethiye, Bodrum, Kusadasi, Ayvalik, etc.