The Chilean Lake District has four distinct seasons inverted from the northern hemisphere. The weather is decisive: in good conditions Puerto Varas is one of the finest places on earth; in bad weather you cannot see the volcano fifty kilometres away and the rain feels permanent.
Summer (December to March) is the obvious choice. Clear days are common, daytime temperatures sit in the low twenties, the days are long, and the volcano shows itself most days. Prices are highest and Chilean tourists are everywhere; book ahead.
Autumn (March to May) has the best light, fewer tourists, lower prices, and the southern beech forests turning red and gold. Rain is more frequent but storms pass through quickly.
Winter (June to August) is wet and grey at lake level but is the season for skiing on Osorno. The volcano often disappears for days behind cloud, then suddenly reappears, freshly snow-coated.
Spring (September to November) is unpredictable — gorgeous days alternating with cold rain. Lupins and wild flowers along the roads in November are spectacular.