When to visit?
Marmara, Aegean, and Mediterranean coasts: These coasts have a typical Mediterranean climate with hot summers and mild winters.
The swimming season becomes shorter the further north one goes: Marmara and North Aegean - June to September; South Aegean and Mediterranean - April to October.
Black Sea Coast: Warm summers, mild winters, and relatively high rainfall.
Central Anatolia: Steppe climate with hot, dry summers; cold winters.
Eastern Anatolia: Long snowy cold winters with mild summers.
Southeast Anatolia: Hot summer with mild, rainy winters.
Source: (Wikitravel)