Spring (April–May) and early autumn (September–October) are the best times to visit. Temperatures are mild, the hills are green, and the town is quiet. Autumn is particularly good if you are interested in foraging — the Parco dell'Adelasia is at its most productive for porcini and truffles from late September through November.
Summer can be warm in the valley, though cooler than the coast. The town is not a major tourist destination so you won't encounter the resort crowds that pack the Riviera in July and August. Winter is cold and quiet, with some snow on the higher Apennine slopes, but the town functions normally year-round.
The Battle of Montenotte anniversary (mid-April) occasionally draws historical re-enactment groups and Napoleon enthusiasts to the area.