Regional differences are also easily recognizable in climatic conditions. Greece has, on the whole, a typical Mediterranean climate with mild and rainy winters and hot and dry summers, but not all with the same characters. On the contrary, the great median chain of the Pindus constitutes a high and difficult to overcome barrier between western and eastern Greece, so as to also determine, between the two, a clear climatic separation. Western Greece is in fact characterized by milder and rainier winters, by greater humidity, by a more intense nebulosity of the atmosphere; Eastern Greece, with colder winters and less rainfall, more frequent snow and frost, greater dryness and greater serenity of the sky. Certainly it has a climate commonly considered as a typical Greek climate. Attica and Athens in particular constitute the most characteristic example.
Athens has an average temperature in the year of 17 °, 3 °, in the coldest month (January) of 8 °, in the hottest month (July) of 27 °. However, the temperature oscillates between winter lows of −10 ° and summer maximums of 41 °, and also the diurnal oscillation is often very strong, with a rapid and relatively intense rise in temperature after cool or cold nights. In winter it often freezes, even if the ice does not last in the afternoon; and on average there are 5 0 6 snowy days. The rains reach just 400 mm. per year, distributed over about 70 rainy days, mostly winter. The dews and the mists are scarce; the sky rarely covered entirely; no more than 30 heavily hazy days a year; and instead about 300 in which, even if a few whitish clouds wadding the sky here and there, this can be said to be serene. Summers, therefore, hot and dry, without any precipitation for continuous periods of 2 months and more, with an almost perfect serenity and purity of the atmosphere: so that, especially in the summer, there is an intense diffused light, for the which the shapes and colors of the landscape stand out clear and sharp. This is the typical climate of Greece.
But if we pass from eastern Greece to western Greece, we find a distinctly different and truly milder climate. The annual thermal averages, in Corfu and Patras, are a little higher than those in Athens due to the higher winter temperatures, which in the average of the coldest month reach and exceed 10 °, while the average of the hottest one is 26 °. And so the lows rarely and not much below zero, and frost is therefore rare, just as snowy days are quite exceptional. But the rains are abundant: about 750 mm. in Patras, and just under 1300 in Corfu, distributed essentially during the winter, over a very large number of days. A higher atmospheric humidity, a more frequent presence of fog, a more intense cloudiness of the sky adds to clearly characterize the climate of western Greece. But along the massive chain from the Pindus to the Taygetos almost interposes a third type of climate essentially characterized by much lower temperatures, by more abundant and largely snowy precipitations: that is, a distinctly alpine climate. Thus a kind of triple climatic zoning is established, such that whoever crosses, p. eg, Greece or the Peloponnese from west to east in March leaves the Ionian coasts in the middle of spring, then has the impression of winter in the mountainous region, and suddenly finds summer along the Aegean coasts. But even in each of these three zones the climatic conditions are not uniform: regardless of the influence of latitude, there are other elements that determine further variety in the climate of Greece. The same jaggedness of the relief determines for each regional unit special climatic characteristics, according to whether the mountainous areas intercept the prevailing winds or not; the effect is especially noticeable, with a colder climate, in those basins which from coastal mountains are closed to the mitigating influences of the sea.