Metz has a continental climate, cold and grey in winter, warm and lively in summer. Late spring through early autumn (May to September) is the best time to visit, with long evenings on the terraces of Place Saint-Louis and outdoor festivals throughout the summer.
The two events worth timing a visit around are the Marché de Noël (late November to late December), one of the best Christmas markets in France, when the centre fills with wooden chalets and lights, and Mirabelles de Metz (mid-August to mid-September), a citywide festival celebrating the local plum with parades, tastings, and concerts.