Thessaloniki’s Mediterranean climate means that winters are warm and rainy, while summers are hot. The best time to go, then, is somewhere in between. Spring and autumn are not excessively hot and if you visit Thessaloniki during either of these seasons, you’ll avoid the bulk of the European vacationers. November through March is when Greece receives most of its rain, so it is best to skip these months if you can.
However, even in winter it is rarely very cold. Sea winds moderate Thessaloniki’s weather, ensuring that seasonal fluctuations in temperature are moderate. Winter temperatures in Thessaloniki average between 5 and 8 degrees Celsius, and in summer this rises to 25 degrees. So if you end up visiting during winter, simply bring along some lightweight rain clothes, waterproof shoes and an umbrella and you should be fine. If you wind up in Thessaloniki during the summer, a good way to escape the heat is to head up to the mountains for a day or two. Higher elevations have much more bearable temperatures during the hottest months.
A good resource to use when you are actually in Thessaloniki is
Do I Need a Jacket?
Check the site before you leave your hotel each morning so you know how warmly you need to dress. Weather Underground’s
is also helpful.