Climate
 
Greece generally has mild wet winters and hot dry summers. Winter temperatures can be severe in the mountains and even Athens can get viciously cold. Maximum temperatures on the islands hover around 30°C (87°F) in summer, but the heat is often tempered by the northerly wind known as the meltemi .
 
The Greece weather is fairly uniform throughout Greece . Due to its geographical position, the weather in Greece and the Greek Islands has mild winters and warm summers, cooled by different kind of seasonal winds. The summers are characterized by sunshine and very little rainfall: great summer holidays guaranted! The Greece weather of the islands of the Aegean and the Ionian seas is milder.Some regions are characterized by the Meltemi, a summer wind which blows mostly the islands of the Aegean and offer perfect wind conditions for sailing and windsurfing.
When To Go
 
Conditions are perfect between Easter and mid-June - beaches and ancient sites are relatively uncrowded; public transport operates on close to full schedules; and accommodation is cheaper and easier to find than in the mid-June to end of August high season. Conditions are once more ideal from the end of August until mid-October, as the season winds down. Winter is pretty much a dead loss outside the major cities as most of the tourist infrastructure goes into hibernation from the middle of October till the beginning of April. This is slowly changing, however; on the most touristy islands, a few restaurants, hotels and bars remain open year-round, while the ski resorts on the mainland do thriving business.
 
Information Courtsey of
https://en.wikipedia.org/wiki/Greece