The park is open year-round but the trekking season runs from October to April. December to February is the peak with the most stable weather, the longest days, and the fullest refugios — book accommodation months in advance. November and March are good shoulder-season options with fewer people and usually decent weather. The Patagonian wind blows hardest from November through January; some days it is genuinely difficult to walk against it.
Winter (June to August) brings snow, closures of some trails, and near-empty refugios — an entirely different and rewarding experience for those prepared for cold and short days. The park never fully closes. The Torres viewpoint hike is best done in midsummer when the light lasts until 10pm; a pre-dawn start for the sunrise is equally worthwhile at any point in the season.