Summer (June–August) is the classic season. The lake is swimmable from late June, hiking conditions are good, and the long evenings are lovely. July and August see the most visitors — not crowds by any urban standard, but the beaches get busy on hot weekends.
Autumn (September–October) is arguably the best time to visit. The Northeast Kingdom's fall foliage is among the most spectacular in New England, and the crisp air makes hiking pleasant. The lake reflections double the colour. Weekends in early October can be busy on the roads, but Westmore itself stays quiet.
Winter brings snowshoeing, ice fishing on the lake, and cross-country skiing in the surrounding forests. The Northeast Kingdom is cold — temperatures well below freezing for weeks at a time — so come prepared. Many local businesses close from November to May.
Spring (April–May) is "mud season" in Vermont: the roads soften, the trails get boggy, and the black flies emerge in late May. Not the ideal time to visit.