Why is Thessaloniki colder than Athens in January?

Thessaloniki is colder than Athens in January primarily due to its geographic location and exposure to regional wind patterns. While Greece generally experiences a Mediterranean climate, the Aegean region is susceptible to low-pressure disturbances that can draw in cold air from the Balkans.

These Balkan regions are sheltered from western influences by the Dinaric mountain system, leaving them open to extreme cold originating from the heart of Eurasia. When these systems move into the Aegean, they bring an icy wind known as the boreas. Consequently, Thessaloníki experiences average January temperatures in the low 40s F (about 6 °C), whereas Athens remains warmer, with averages in the low 50s F (about 10 °C).1