The best time to visit Thessaloniki is April to June or September to October, when temperatures are comfortable (18–27°C), the city is lively but not overwhelmed, and the countryside around it is at its most photogenic.
Spring (April–May): The ideal window. Wildflowers cover the slopes of Olympus, Halkidiki beaches are uncrowded, and the city's outdoor café terraces fill up with locals enjoying post-winter air. Rainfall is possible but rarely persistent.
Summer (June–August): July and August are hot (frequently 35°C+), but the city stays active. This is the best time for Halkidiki beaches, though the peninsula gets very busy. The Thessaloniki International Film Festival takes place in November — but summer brings outdoor concerts and the Sani Festival on Halkidiki.
Autumn (September–October): September is arguably the sweetest spot — the Aegean is still warm enough to swim, the heat has eased, grapes are being harvested in the nearby Naoussa wine region, and hotel prices drop significantly.
Winter (November–March): Cold and occasionally snowy, but Thessaloniki handles it with grace. The Christmas market on Aristotelous Square is charming, museums are crowd-free, and hotel rates are at their lowest. Skiing at Seli or Vermio resorts is possible from December.