June through September is winter and the ski season. Cerro Catedral runs full operations, the town is full, and prices are high. Snow on the streets is normal in July and August. Pack for serious cold — overnight lows go well below freezing.
December through March is summer. The lake warms enough to swim (just), the trails open up at altitude, and the days stretch to nearly 10pm light. January and February are the busiest summer weeks, with Argentine families on holiday — book everything ahead.
The shoulder seasons are the secret. April turns the lengas and ñires forests dark red and gold. November is fly-fishing season, with wildflowers along the lakeshore and few tourists. Late May and early June is the egresados period when school graduation trips fill the town — fun if you are young, exhausting if you are not.