Valdivia is in the heart of southern Chile's wet zone — it receives over 2,000mm of rain per year, which is why the forests are so lush and the rivers so full. January and February are the driest months and the most pleasant for outdoor activities, river trips, and visits to the coast. December and March are also reasonable. The rest of the year is genuinely rainy — not unpleasant for a short visit to the markets and museums, but limiting for active outdoor plans.
The Valdivian summer carnival (January) brings music and events to the city centre and is a lively time to visit. The university keeps the city young and active year-round. Winter (June-August) is cold and wet, but the city doesn't shut down — the cafes fill up, the markets continue, and the breweries are as welcoming as ever.