October is the best month: the larch and birch forest below the treeline turns gold and red, the peaks are typically clear, and the glacial lakes are at their most vivid colour. The high visitor numbers in October are the price of these optimal conditions. Late September and early November are similar but progressively colder and quieter.
Spring (April and May) is the second-best season — fewer visitors, the lakes are clear, and wildflowers appear on the lower slopes. Summer (June through August) brings occasional monsoon cloud and more visitors but is not unpleasant. Avoid December through March: snow makes the upper trails impassable, the entrance road can close in bad weather, and the altitude is genuinely dangerous in cold conditions for those not properly equipped.