Athens has a Subtropical Mediterranean climate (Köppen climate classification Csa) while the southern Athens area experiences a hot Semi-arid climate (Köppen climate classification BSh), with extremely long periods of sunshine throughout the year (2884 hours of sunshine per year at Thision meteorological station 1961-1990) and with the greatest amounts of precipitation mainly occurring from mid-October to mid-April; any precipitation is sparse during summer and it generally takes the form of showers and/or thunderstorms. Due to its location in a rain shadow because of Mount Parnitha, the Athenian climate is much drier compared to most of the rest of Mediterranean Europe. The mountainous northern suburbs, for their part, experience a somewhat differentiated climatic pattern, with generally lower temperatures. Fog is highly unusual in the city centre but it is more frequent to the east, behind the Hymettus mountain range.

Winter is mild, with a January average of 8.9 °C (48.0 °F); in Nea Filadeflia and 10.3 °C (50.5 °F) in Hellenikon; Snowfalls are not common and these do not normally lead to significant, if any, disruption. Nonetheless, the city has experienced heavy snowfalls in the past decade. During the blizzards of March 1987; February 1992; 4-6 January 2002; 12-13 February 2004; January 2006; and 16-18 February 2008, snow blanketed large parts of the metropolitan area, causing havoc across much of the city.

Spring and fall (autumn) are considered ideal seasons for sightseeing and all kinds of outdoor activities.

Summers can be particularly hot and at times prone to smog and pollution related conditions (however, much less so than in the past). According to the National Observatory of Athens the average daytime maximum temperature in Thision (period 2001-2009) for the month of July is 35.1 °C (95.2 °F)

Athens is notorious for its heatwaves occurring generally during the months of July and/or August, when hot air masses sweep across Greece from the south or the southwest. On such days temperatures soar over 38 °C (100 °F).