The coldest Christmas Day on record at the historic climate station of the National Observatory of Athens (NAO) occurred on December 25, 1909. This station, located permanently on the Hill of the Nymphs in Thiseion, has been providing continuous weather data for Athens since 1890. Typically, December temperatures in Athens hover around 10°C, making snowfall on Christmas Day a rare event—though it has occurred a few times over the past 125 years, mostly during the early decades of the 20th century, according to ClimateHub, Greece’s information hub for national energy needs and renewable energy.

Based on temperature records maintained by the station and reported by the author team (Stergios Misios, Dimitra Founta, Roula Costa), the coldest Christmas Day in the last 125 years was December 25, 1909, according to the Julian calendar (January 7, 1910, in the Gregorian calendar adopted in 1923). This record holds even when considering the average daily temperature across December 24, 25, and 26 of that year.

On that day, the average temperature did not rise above 4°C, and night temperatures dropped to as low as 2°C.

Other notably cold Christmases include the years 1933, 1937, 1953, 1986, 1987, and 1992, with average temperatures around 5°C and significantly colder nights. Despite the chill, snowfall was not consistently recorded in central Athens during these periods, although it may have fallen in the northern parts of the basin. In contrast, heavy snowfall was observed in Athens on the night leading into December 25, 1949, with other snow events recorded on December 24–26 in years such as 1903, 1906, 1907, 1913, 1915, 1936, 1948, 1962, 1968, 1991, and 1992.

Of particular note was the harsh winter from December 27, 1941, to January 5, 1942, when Athens experienced ten consecutive nights below freezing, with a low of -4.4°C on January 2. This severe cold was an additional hardship for Athenians already struggling with frost and hunger during the Occupation, ClimateHub highlights.

Using modern climate reanalysis tools—which combine climate models and historical weather station data—researchers can reconstruct past weather patterns for the Southeastern Mediterranean region. For example, the chilly Christmas of 1909 corresponded to a cold air invasion from the northeast, starting on December 24 and maintaining low temperatures throughout the holiday period, not only in Athens but across Greece down to Crete. This is supported by early 20th-century meteorological data from regional stations maintained by the National Observatory (the Aeginitis Network). On Christmas Day 1909, Syros recorded a maximum temperature of 9°C, while Lamia reached only 4°C, dropping to -2°C at night, though without snowfall.

On the other end of the spectrum, Christmas 2010 felt more like summer, with an average daily temperature of 17°C and a high of 19°C; Christmas Eve was even warmer, peaking at 22°C. Similar mild Christmas weather was observed in northern Greece and the Balkans, as confirmed by past climate reanalysis. Spring-like conditions were also experienced at Christmas in 1995 and 1927. Notably, while the morning of December 25, 1927, was dull and rainy, conditions improved by afternoon, leading to a lively holiday atmosphere, as described in the newspaper Empros on December 27, 1927. More recently, Christmas 2023 also reminded Athenians of spring, with a maximum temperature of 22°C on Christmas Eve, ClimateHub notes.