It is really hard to generalize the climate of Turkey. It just “depends” on where and when you will be going. In winter time in eastern cities, the temperature goes down to -20Â°C in day time, while in southern cities it is 20Â°C. In summer time Turkey is generally warm, varying between 25Â°C and 40Â°C in day time.
If you are planning to visit Istanbul, summer and spring is the best time. It is warm and humid, but it is bright all around, perfect for sight-seeing. Average summer temperature is about 30Â°C in day time. On the other hand, in winter time it is generally cloudy and rainy, average temperature of 10Â°C (rarely goes down to 0Â°C and snows); causing a depressive mood.
For a seaside holiday, you have two choices: western and southern coasts. There are more accommodation options in southern coast, especially in Antalya region; but the weather is warmer and more humid compared to the western coast (Avarage of 35Â°C in Antalya, 30Â°C in western cities). In southern coast, the sunny weather and sea season may extend from April to December; so it may be reasonable to have an early or a late holiday.
Spring is the best time for travelling midland and eastern cities, since it is too warm in summer and too cold and snowy in winter. Summer is the best option for nature trails by the Black Sea coast. It may be chilling and rainy during spring and fall.