Pamukkale is located in Aegean region of Turkey but far from Aegean Sea. Aegean Coastal plain has mild climate, warm winters, sunny autums, springs and hot summers. Inland part of Aegean Region is cooler than seaside.
Mountains in this region are perpendicular to the Aegean Sea so interior part is open to winds coming from sea. Winters are mild, even in January and February sometimes it is sunny and pleasant, but mostly rainy just sometimes snowy.
For visiting and exploring Hierapolis in Pamukkale autumn and spring are the most inviting months.