Bumthang sits high — Jakar is at around 2,600 metres — and winters are sharp. Snow is possible from December to February, with temperatures regularly below freezing at night. Spring (March to May) and autumn (September to November) are the best months, with clear skies, warm days, and cool nights.
Autumn is the festival season. The Jambay Lhakhang Drup (usually late October or early November) is the most famous, with masked dances and the rare midnight Tercham. Around the same time the Thangbi Mani and Tamshing Phala festivals take place at the nearby monasteries. If you can plan a visit to overlap with one of these, do it — they are among the most authentic religious festivals in Bhutan and far less crowded than the big tsechus in Thimphu and Paro.
Summer (June to August) is the monsoon — rain, mist, and leeches in the forest tracks — though the valley remains green and the apple harvest begins in August.