Belgium enjoys a fairly standard temperate climate, with warm – if mild – summers and moderately cold winters. Generally speaking, temperatures rise the further south you go, with Wallonia a couple of degrees warmer than Flanders for most of the year, though in the east this is offset by the more severe climate of continental Europe, and emphasized by the increase in altitude of the Ardennes. Rain is always a possibility, though you can expect a greater degree of precipitation in the Ardennes and upland regions than on the northern plains.
The cities of Belgium are all-year tourist destinations, though you might think twice about visiting Bruges, the region’s most popular spot, during August, when things get mighty crowded. Flanders as a whole is best visited any time between early spring and late autumn, though winter has its advantages too – iced canals and hoarfrost polders – if you don’t mind the short hours of daylight. Wallonia, especially the Ardennes, is more seasonal, with many things closing down in the winter, so try to visit between April and October.