Neuchâtel is a year-round city, but summer (June to September) is the obvious peak. The lake is swimmable, the vineyards along the north shore are in full leaf, and the outdoor terraces are busy. The Wednesday and Saturday markets are good in all seasons, but best in summer and autumn when the local produce is at its peak.
Autumn is exceptional here. The Jura hills turn gold in October, the wine harvest runs from mid-September to mid-October (you can often watch or participate in the vendange in the lakeside villages), and the light on the lake on clear autumn mornings is remarkable.
Winter is quieter and colder — the Jura can get significant snow — but the city is never dead. The museums are fully operational, the fondue is at its most appropriate, and Neuchâtel empties of the summer crowds in a way that makes it easier to feel like a resident rather than a tourist.
Spring is short but beautiful, with the vines beginning to show green in April and the lake reflecting sharp mountain views before the summer haze settles.