Athens has a hot-summer Mediterranean climate . The dominant feature of Athens’ climate is alternation between prolonged hot and dry summers because of the dry and hot winds blowing from the Sahara, and mild, wetter winters with moderate rainfall, due to the westerly winds. With an average of 451 millimetres (17.8 in) of yearly precipitation, rainfall occurs largely between the months of October and April. July and August are the driest months when thunderstorms occur sparsely. Furthermore, some coastal areas of Athens, known as the Athens Riviera have a hot semi-arid climate (BSh) according to the climate atlas published by the Hellenic National Meteorological Service. However, places like Elliniko, which are classified as hot semi deserts(köppen; Bsh), because of the low annual rainfall, haven’t recorded temperatures so high as in other places in the city. This happens because of the moderating sea and the fact that there is no such industrialization there, compared to other regions of the city.
Owing to the rain shadow of the Pindus Mountains, annual precipitation of Athens is lower than most other parts of Greece, especially western Greece. As an example, Ioannina receives around 1,300 mm (51 in) per year, and Agrinio around 800 mm (31 in) per year. Daily average highs for July have been measured around 34 °C or 93 °F in downtown Athens, but some parts of the city may be even hotter for the higher density of buildings, and the lower density of vegetation, such as the center, in particular, western areas due to a combination of industrialization and a number of natural factors, knowledge of which has existed since the mid-19th century. Due to the large area covered by Athens Metropolitan Area, there are notable climatic differences between parts of the urban conglomeration. The northern suburbs tend to be wetter and cooler in winter, whereas the southern suburbs are some of the driest locations in Greece and record very high minimum temperatures in summer. Snowfall is infrequent and it generally occurs once a year. The last time snow fell in Athens was 16 February 2021; snow blanketed the city from the north to the very south suburbs with depth ranges from 10 cm to 25 cm.
Athens is affected by the urban heat island effect in some areas which is caused by human activity, altering its temperatures compared to the surrounding rural areas, and leaving detrimental effects on energy usage, expenditure for cooling, and health. The urban heat island of the city has also been found to be partially responsible for alterations of the climatological temperature time-series of specific Athens meteorological stations, because of its impact on the temperatures and the temperature trends recorded by some meteorological stations. On the other hand, specific meteorological stations, such as the National Garden station and Thiseio meteorological station, are less affected or do not experience the urban heat island.
Athens holds the World Meteorological Organization record for the highest temperature ever recorded in Europe, at 48 °C (118.4 °F), which was recorded in the Elefsina and Tatoi suburbs of Athens on 10 July 1977.