Spring and autumn are the best seasons. April through June brings green lower-valley growth and relatively stable weather, though late spring afternoons can produce thunderstorms. September and October are the most popular months — the larch and fir forests in the valleys turn gold and the skies are clearest after the summer monsoon retreats.
Summer brings reliable afternoon thunderstorms and the highest visitor numbers; the views are nonetheless often clear in the morning. Winter closes the upper valleys from December through February, temperatures drop to -15°C at altitude, and snowfall can make the lower trails slippery, but the park is quieter and the snow on the peaks is extraordinary. The entrance fees drop in the low season.