Spring can come as early as March as it did in 2005 or it can be delayed until the end of April. After that it steadily gets warmer and in June even the most timid are willing to swim. Bathers can continue to swim all through the month of September usually and often into mid-October as well. Spring has several plus sides to it that high summer doesn't enjoy:
In southern Greece It may still rain in spring but only for a couple of hours and the sun invariably comes out to dry things off. In Northern Greece it will likely remain cold from November to April with snow in the west and in the mountains.
In the official summer period the southern Grecian climate is arid, if not down right drought like, and hot. The wind is something most visitors don't expect and can blow spring or summer especially on the islands.
Because Greece is such a varied country its difficult to make accurate predictions. The dry hot conditions of southern Crete don't compare well with the high altitude mountains of Northern Greece. Of course it holds true that the farther south one goes the warmer it gets but because Greece is situated at the juncture between the Mid-East, the Balkans and N. Africa climate conditions become more complicated.
During summer its fair to say it will generally be warm because the intense heat concentrated in the middle East causes dry European air to be drawn down from the north and cover the Eastern Mediterranean. This Northern wind is known as the Meltemi wind and its most common during the long, hot, endless summer months of June, July and August. The Aegean islands in particular experience the Meltemi which, as mentioned elsewhere, can cause ferry boat delays and cancellations in summer!
In Greece spring and fall are hard to define as the temperatures and conditions can vary considerably. Winters may have long stretches of warm and placid weather in the north while southern areas may have more salubrious weather in February or November than in April. The end of March in Crete may be violently windy one day and three days later a warm 70F.
By late April however the weather has usually come around to more warm and settled conditions. The hotter it is the more there is going on in Greece. Augusts is high season and reservations should be made well in advance.
Greece has a Mediterranean climate with plenty of sunshine, mild
temperatures and a limited amount of rainfall. Due to the country's
geographical position, its rugged relief and its distribution between
the mainland and the sea, there is great variation in Greece's climate.
In summer, the dry hot days are cooled by seasonal winds called the
meltemi, while mountainous regions have generally lower temperatures.
The winters are mild in lowland areas, with a minimum amount of snow and
ice, yet, mountains are usually snow-covered. Moreover, a common
phenomenon is the occurrence of different climactic conditions during
the same season (for instance, mild heat in coastal areas and cool
temperatures in mountainous regions).
Greece's main meteorological data are given below (Source: National
Average temperatures (°C)
Relative humidity (%)
Average daily sunshine (in hours)